Scaphoid kinematics in vivo

In vivo non-contact regions of proximal scaphoid in six extreme wrist positions

INTRODUCTION

Fractures of the scaphoid are the most common carpal injuries, account for 80-90% of all carpal fractures. 5-15% nonunion of scaphoid fractures were reported even with adequate primary treatment, which probably progresses to osteoarthritic changes several decades later. Researches regarding to scaphoid physiological characteristic in vitro and in vivo and kinds of trials in clinical practice are being kept on going, which contribute much to our clinical practice. With the advancing wrist arthroscopy, 3D-print patient-specific drill guide, and intraoperative fluoroscopic guidance, dorsal approach (mini-invasive and percutaneous technique) is being popular, through which we can implant the screw in good coincidence with biomechanics and with less disturbing tenuous blood supply of the scaphoid. Investigating the noncontact area of the dorsal proximal scaphoid in different wrist positions can facilitate preoperatively estimating insert point of the screw.

MATERIALS AND METHODS

Eight volunteers were recruited to accept CT scans in six extreme wrist positions. The images of DICOM mode were imput into the Mimics analytical system, the segmented scaphoid, lunate and radius were exported in mode of ASCII STL and were opened in the software of Geomagic studio. We created four planes based on anatomic markers on the surface of the radius and scaphoid to confine the proximal scaphoid to form the so-called non-contact regions. We measured and compared the areas in six targeted positions.

RESULTS

Amidst six extreme wrist positions, area of the non-contact region in extreme dorsal extension (59.81 ± 26.46 mm2) was significantly the smallest, and it in extreme palmar flexion significantly was largest (170.51 ± 30.44 mm2). The non-contact regions increased in order of dorsal extension, supination, ulnar deviation, radial deviation, pronation and palmar flexion. As for two-group comparison, the non-contact region showed significantly larger (p < 0.05) in palmar flexion than the others except for in pronation individually, and in radial deviation (p < 0.05) than in dorsal extension.

CONCLUSIONS

Sufficient space was available for the screw started from the dorsal approach despite the wrist positions.

Dynamic assessment of scapholunate ligament status by real-time magnetic resonance imaging: an exploratory clinical study

OBJECTIVE

Clinical-standard MRI is the imaging modality of choice for the wrist, yet limited to static evaluation, thereby potentially missing dynamic instability patterns. We aimed to investigate the clinical benefit of (dynamic) real-time MRI, complemented by automatic analysis, in patients with complete or partial scapholunate ligament (SLL) tears.

MATERIAL AND METHODS

Both wrists of ten patients with unilateral SLL tears (six partial, four complete tears) as diagnosed by clinical-standard MRI were imaged during continuous active radioulnar motion using a 1.5-T MRI scanner in combination with a custom-made motion device. Following automatic segmentation of the wrist, the scapholunate and lunotriquetral joint widths were analyzed across the entire range of motion (ROM). Mixed-effects model analysis of variance (ANOVA) followed by Tukey's posthoc test and two-way ANOVA were used for statistical analysis.

RESULTS

With the increasing extent of SLL tear, the scapholunate joint widths in injured wrists were significantly larger over the entire ROM compared to those of the contralateral healthy wrists (p<0.001). Differences between partial and complete tears were most pronounced at 5°-15° ulnar abduction (p<0.001). Motion patterns and trajectories were altered. Complete SLL deficiency resulted in complex alterations of the lunotriquetral joint widths.

CONCLUSION

Real-time MRI may improve the functional diagnosis of SLL insufficiency and aid therapeutic decision-making by revealing dynamic forms of dissociative instability within the proximal carpus. Static MRI best differentiates SLL-injured wrists at 5°-15° of ulnar abduction.

Two Parallel Headless Compression Screws for Scaphoid Fractures: Radiographic Analysis and Preliminary Outcome

BACKGROUND

Despite surgical fixation, the scaphoid nonunion rate remains at 3% to 5%. Recent biomechanical studies have demonstrated increased stability with 2-screw constructs. The objective of our study is to determine the preliminary union rate and anatomic feasibility of 2-screw surgical fixation for scaphoid fractures.

METHODS

This study is a retrospective case series of 25 patients (average age 32 years) with scaphoid fractures treated with 2 parallel headless compression screws (HCS). Postoperative evaluation included Mayo Wrist Score (MWS), range of motion, time to union, and return to activity. Bivariate analysis for gender and Pearson correlation coefficient for body size (height, weight, and body mass index) was conducted against radiographically measured scaphoid width, screw lengths, and the distance between the 2 screws.

RESULTS

All fractures healed with an average time to union of 9.9 weeks (median 7.6 weeks; range: 4.1-28.3). The mean MWS was 93.3 (range: 55-100), with 3 complications (12%), one of which affected the outcome of the surgery. The bivariate analysis demonstrated that the female gender was associated with significantly smaller scaphoid width (P = .004) but a similar distance between the 2 screws (P = .281). The distance between the 2 screws and the body size demonstrated a weak-to-no correlation.

CONCLUSIONS

The 2-screw construct for scaphoid fracture achieved a favorable union rate and clinical outcome. Gender was the only variable significantly associated with scaphoid width and screw length. The distance between the screws was constant regardless of gender and body size, indicating that the technique for parallel screw placement can remain consistent.

TYPE OF STUDY

Therapeutic.

LEVEL OF EVIDENCE

Level IV.

Double screw versus angular stable plate fixation of scaphoid waist nonunions in combination with intraoperative extracorporeal shockwave therapy (ESWT)

INTRODUCTION

Over the past years, different fixation techniques focused on rotational stability in order to increase stability and stimulate union rates. Additionally, extracorporeal shockwave therapy (ESWT) has gained importance in the treatment of delayed and nonunions. Purpose of this study was to compare the radiological and clinical outcome of two headless compression screws (HCS) and plate fixation in scaphoid nonunions, in combination with intraoperative high energy ESWT.

MATERIALS AND METHODS

Thirty-eight patients with scaphoid nonunions were treated by using a nonvascularized bone graft from the iliac crest and stabilization with either two HCS or a volar angular stable scaphoid plate. All patients received one ESWT session with 3000 impulses and energy flux per pulse of 0.41 mJ/mm² intraoperatively. Clinical assessment included range of motion (ROM), pain according to the Visual Analog Scale (VAS), grip strength, disability of the Arm Shoulder and Hand Score, Patient-Rated Wrist Evaluation Score, Michigan Hand Outcomes Questionnaire and modified Green O'Brien (Mayo) Wrist Score. To confirm union, a CT scan of the wrist was performed.

RESULTS

Thirty-two patients returned for clinical and radiological examination. Out of these, 29 (91%) showed bony union. All patients treated with two HCS compared to 16 out of 19 (84%) patients treated by plate showed bony union on the CT scans. The difference was not statistically significant. However, at a mean follow-up interval of 34 months, no significant differences could be found in ROM, pain, grip strength and patient-reported outcome measurements between the two HCS and plate group. Height-to-length ratio and capitolunate angle improved significantly in both groups compared to preoperative.

CONCLUSIONS

Scaphoid nonunion stabilization by using two HCS or angular stable volar plate fixation and intraoperative ESWT results in comparable high union rates and good functional outcome. Due to the higher rate for a secondary intervention (plate removal), HCS might be preferable as first choice, whereas the scaphoid plate fixation should be reserved for recalcitrant (substantial bone loss, humpback deformity or failed prior surgical intervention) scaphoid nonunions.

Double-Screw Osteosynthesis in an Unstable Scaphoid Fracture Model: A Biomechanical Comparison of Two Screw Configurations

PURPOSE

Although there is evidence that a single headless compression screw is sufficient for fixation of most scaphoid fractures, double-screw osteosynthesis has been shown to result in higher failure strength and stiffness than a single screw. However, the biomechanical effect of different screw configurations has not been determined.

METHODS

A standardized unstable fracture model was produced in 28 cadaveric scaphoids. Specimens were randomly allocated to 1 of 2 fixation groups using 2 internal compression screws positioned in either the sagittal or coronal plane. A specimen-specific 3-dimensionally-printed customized screw placement and osteotomy device was developed using computer-aided design-generated models derived from computed tomography scan data of each individual scaphoid. Load to failure and stiffness of the repair constructs were evaluated using a mechanical testing system.

RESULTS

There were no significant differences in size, weight, and density between the scaphoid specimens. The average distance between screws was significantly greater in the sagittal group than in the coronal group. There were no significant differences between the coronal and sagittal aligned double screws in load to 2 mm displacement (mean coronal 180.9 ± 109.7 N; mean sagittal 156.0 ± 85.8 N), load to failure (mean coronal 275.9 ± 150.6 N; mean sagittal 248.0 ± 109.5 N), stiffness (mean coronal 111.7 ± 67.3 N/mm; mean sagittal 101.2 ± 45.1 N/mm), and energy absorption (mean coronal 472.6 ± 261.4 mJ; mean sagittal 443.5 ± 272.7 mJ).

CONCLUSIONS

There are no significant biomechanical differences between the sagittal or coronal aligned double headless compression screws in a scaphoid fracture model with bone loss.

CLINICAL RELEVANCE

In cases where double-screw fixation of the scaphoid is being considered, the placement of double screws can be at the discretion of the surgeon, and can be dictated by ease of access, surgical preference, and fracture orientation.

Single Versus Dual Headless Compression Screw Fixation of Scaphoid Nonunions: A Biomechanical Comparison

BACKGROUND

Management of scaphoid nonunions with bone loss varies substantially. Commonly, internal fixation consists of a single headless compression screw. Recently, some authors have reported on the theoretical benefits of dual-screw fixation. We hypothesized that using 2 headless compression screws would impart improved stiffness over a single-screw construct.

METHODS

Using a cadaveric model, we compared biomechanical characteristics of a single tapered 3.5- to 3.6-mm headless compression screw with 2 tapered 2.5- to 2.8-mm headless compression screws in a scaphoid waist nonunion model. The primary outcome measurement was construct stiffness. Secondary outcome measurements included load at 1 and 2 mm of displacement, load to failure for each specimen, and qualitative assessment of mode of failure.

RESULTS

Stiffness during load to failure was not significantly different between single- and double-screw configurations (P = .8). Load to failure demonstrated no statistically significant difference between single- and double-screw configurations. Using a qualitative assessment, the double-screw construct maintained rotational stability more than the single-screw construct (P = .029).

CONCLUSIONS

Single- and double-screw fixation constructs in a cadaveric scaphoid nonunion model demonstrate similar construct stiffness, load to failure, and load to 1- and 2-mm displacement. Modes of failure may differ between constructs and represent an area for further study. The theoretical benefit of dual-screw fixation should be weighed against the morphologic limitations to placing 2 screws in a scaphoid nonunion.

Anatomy, Biomechanics, and Loads of the Wrist Joint

The wrist is by far the most differentiated section of the musculoskeletal system. The spectrum of wrist injuries ranges from minor injuries to complex traumas with simultaneous loss of functions, resulting in enormous economic costs. A proper understanding of the anatomy and biomechanics is essential for effective treatment, whether conservative or surgical; this applies to the wrist no less than to other parts of the human body. Here; information on the wrist anatomy; kinematics; and biomechanical behavior is presented, commencing with a brief explanation of the structure of its hard and soft tissues. Eight carpal bones in combination with two forearm bones (radius and ulna) construct the wrist joint. The motion of the wrist joint is initiated by the muscles of the forearm, and strong and short ligaments ensure the stability of the wrist. All of these components are essential to bringing functions to the wrist joint because these structures allow wrist mobility and sustainability. In addition, the kinematics of the wrist joint is presented and different biomechanical model approaches. The therapeutic (surgical) restoration of the balance between the load–bearing capacity and the actual stress on a joint is the prerequisite for a lifelong and trouble-free function of a joint. Regarding the complex clinical problems, however, a valid biomechanical wrist joint model would be necessary as assistance, to improve the success of systematized therapies based on computer–aided model–based planning and intervention.

Understanding the Patterns of Deformity of Wrist Fractures Using Computer Analysis

Computer modeling of the wrist has followed other fields in the search for descriptive methods to understand the biomechanics of injury. Using patient-specific 3D computer models, we may better understand the biomechanics of wrist fractures in order to plan better care. We may better estimate fracture morphology and stability and evaluate surgical indications, design more adequate or effective surgical approaches and develop novel methods of therapy. The purpose of this review is to question the actual advances made in the understanding of wrist fractures using computer models.

Predicting Carpal Bone Kinematics Using an Expanded Digital Database of Wrist Carpal Bone Anatomy and Kinematics

The wrist can be considered a 2 degrees-of-freedom joint with all movements reflecting the combination of flexion-extension and radial-ulnar deviation. Wrist motions are accomplished by the kinematic reduction of the 42 degrees-of-freedom of the individual carpal bones. While previous studies have demonstrated the minimal motion of the scaphoid and lunate as the wrist moves along the dart-thrower's path or small relative motion between hamate-capitate-trapezoid, an understanding of the kinematics of the complete carpus across all wrist motions remains lacking. To address this, we assembled an open-source database of in vivo carpal motions and developed mathematical models of the carpal kinematics as a function of wrist motion. Quadratic surfaces were trained for each of the 42-carpal bone degrees-of-freedom and the goodness of fits were evaluated. Using the models, paths of wrist motion that generated minimal carpal rotations or translations were determined. Model predictions were best for flexion-extension, radial-ulnar deviation, and volar-dorsal translations for all carpal bones with R ²  > 0.8, while the estimates were least effective for supination-pronation with R ²  < 0.6. The wrist path of motion's analysis indicated that the distal row of carpal bones moves rigidly together (<3° motion), along the anatomical axis of wrist motion, while the bones in the proximal row undergo minimal motion when the wrist moves in a path oblique to the main axes. The open-source dataset along with its graphical user interface and mathematical models should facilitate clinical visualization and enable new studies of carpal kinematics and function. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2661-2670, 2019.

Differences in the Rotation Axes of the Scapholunate Joint During Flexion-Extension and Radial-Ulnar Deviation Motions

PURPOSE

To determine the location of the rotation axis between the scaphoid and the lunate (SL-axis) during wrist flexion-extension (FE) and radial-ulnar deviation (RUD).

METHODS

An established and publicly available digital database of wrist bone anatomy and carpal kinematics of 30 healthy volunteers (15 males and 15 females) in up to 8 different positions was used to study the SL-axis. Using the combinations of positions from wrist FE and RUD, the helical axis of motion of the scaphoid relative to the lunate was calculated for each trial in an anatomical coordinate system embedded in the lunate. The differences in location and orientation between each individual axis and the average axis were used to quantify variation in axis orientation. Variation in the axis location was computed as the distance from the closest point on the rotation axis to the centroid of the lunate.

RESULTS

The variation in axis orientation of the rotation axis for wrist FE and RUD were 84.3° and 83.5°, respectively. The mean distances of each rotation axis from the centroid of the lunate for FE and RUD were 5.7 ± 3.2 mm, and 5.0 ± 3.6 mm, respectively.

CONCLUSIONS

Based on the evaluation of this dataset, we demonstrated that the rotation axis of the scaphoid relative to the lunate is highly variable across subjects and positions during both FE and RUD motions. The range of locations and variation in axis orientations in this data set of 30 wrists shows that there is very likely no single location for the SL-axis.

CLINICAL RELEVANCE

Scapholunate interosseous ligament reconstruction methods focused on re-creating a standard SL-axis may not restore what is more likely to be a variable anatomical axis and normal kinematics of the scaphoid and lunate.

Treatment of scaphoid waist nonunion by one, two headless compression screws or plate with or without additional extracorporeal shockwave therapy

INTRODUCTION

Scaphoid nonunion remains challenging for hand surgeons. Several treatment options are available such as: non-vascularized or vascularized bone grafting, with or without additional stabilization. In the last few decades, extracorporeal shockwave therapy (ESWT) has become an established procedure for treating delayed and nonunions. Purpose of this retrospective follow-up study was (a) to investigate union rate and clinical outcome of the different implants [either one/two headless compression screws (HCS) or a plate] and (b) union rate and clinical outcome using only surgery, or a combination of surgery and ESWT.

MATERIALS AND METHODS

The study included 42 patients with scaphoid nonunions of the waist with a mean follow-up of 52 months. All patients received a non-vascularized bone graft from the iliac crest and stabilization was achieved by using one, two HCS or a plate. ESWT was performed with 3000 impulses, energy flux density per pulse 0.41 mJ/mm² within 2 weeks after surgery. Clinical assessment included range of motion (ROM), pain according to the Visual Analog Scale (VAS), grip strength, Disability of the Arm Shoulder and Hand Score, Patient-Rated Wrist Evaluation Score, Michigan Hand Outcomes Questionnaire and modified Green O'Brien (Mayo) Wrist Score. In addition, each patient had a CT scan of the wrist.

RESULTS

A total of 33/42 (79%) patients showed union at the follow-up investigation. Patients treated with additional ESWT showed bony healing in 21/26 (81%) and without ESWT in 12/16 (75%). Patients that were stabilized using one HCS showed bony healing in 6/10 (60%), with two HCS 10/12 (83%) and by plate 17/20 (85%). The ESWT group had a significantly lower pain score according to the VAS and better modified Green O'Brien (Mayo) Score. No differences could be found in respect of ROM, grip strength, functional outcome score depending of which stabilization method was used.

CONCLUSIONS

Stabilization of scaphoid waist nonunions with two HCS or plate showed higher union rates than a stabilization using only one HCS. In addition, ESWT combined with a nonvascularized bone graft from the iliac crest seems a suitable option for treating scaphoid nonunions.

Trabecular bone patterning across the human hand

Hand bone morphology is regularly used to link particular hominin species with behaviors relevant to cognitive/technological progress. Debates about the functional significance of differing hominin hand bone morphologies tend to rely on establishing phylogenetic relationships and/or inferring behavior from epigenetic variation arising from mechanical loading and adaptive bone modeling. Most research focuses on variation in cortical bone structure, but additional information about hand function may be provided through the analysis of internal trabecular structure. While primate hand bone trabecular structure is known to vary in ways that are consistent with expected joint loading differences during manipulation and locomotion, no study exists that has documented this variation across the numerous bones of the hand. We quantify the trabecular structure in 22 bones of the human hand (early/extant modern Homo sapiens) and compare structural variation between two groups associated with post-agricultural/industrial (post-Neolithic) and foraging/hunter-gatherer (forager) subsistence strategies. We (1) establish trabecular bone volume fraction (BV/TV), modulus (E), degree of anisotropy (DA), mean trabecular thickness (Tb.Th) and spacing (Tb.Sp); (2) visualize the average distribution of site-specific BV/TV for each bone; and (3) examine if the variation in trabecular structure is consistent with expected joint loading differences among the regions of the hand and between the groups. Results indicate similar distributions of trabecular bone in both groups, with those of the forager sample presenting higher BV/TV, E, and lower DA, suggesting greater and more variable loading during manipulation. We find indications of higher loading along the ulnar side of the forager sample hand, with high site-specific BV/TV distributions among the carpals that are suggestive of high loading while the wrist moves through the 'dart-thrower's' motion. These results support the use of trabecular structure to infer behavior and have direct implications for refining our understanding of human hand evolution and fossil hominin hand use.

A three-dimensional printed patient-specific scaphoid replacement: a cadaveric study

We present our first cadaveric test results of a three-dimensional printed patient-specific scaphoid replacement with tendon suspension, which showed normal motion behaviour and preservation of a stable scapholunate interval during physiological range of motion.

Length Changes in Scapholunate Interosseous Ligament With Resisted Wrist Radial and Ulnar Inclination

PURPOSE

To investigate the changes in length of the scapholunate interosseous ligament (SLIL) when the wrist is resisting horizontal lateral load and the forearm is in full pronation in vivo.

METHODS

We obtained computed tomography scans of the wrists of 6 volunteers in 3 situations: 0° position (0° extension and 0° ulnar inclination) and full forearm pronation without force, and in the same position but with resisted ulnar and radial deviation. Nine zones of 3 subregions of the SLIL were measured and analyzed with computer modeling.

RESULTS

Changes in length of the palmar SLIL with resisted ulnar deviation were significantly greater than those without an applied lateral load. In contrast, the changes in length of the dorsal SLIL with resisted radial deviation were statistically greater than those in the 0° position without loading. However, no significant differences in the changes in length of the proximal SLIL were found in any of 3 situations, except the dorsal zone with resisted radial deviation.

CONCLUSIONS

Application of lateral load has an effect on the separation of the palmar and dorsal insertions of the SLIL. The palmar subregion of the SLIL was more highly strained with wrist-resisted ulnar deviation. Conversely, the dorsal subregion of the SLIL was under greater tension with wrist-resisted radial deviation.

CLINICAL RELEVANCE

For patients undergoing nonsurgical treatment of SLIL tears, a sudden contraction of ulnar or radial deviation agonist muscles may be harmful and contribute to SL instability.

Does Wrist Laxity Influence Three-Dimensional Carpal Bone Motion?

Previous two-dimensional (2D) studies have shown that there is a spectrum of carpal mechanics that varies between row-type motion and column-type motion as a function of wrist laxity. More recent three-dimensional (3D) studies have suggested instead that carpal bone motion is consistent across individuals. The purpose of this study was to use 3D methods to determine whether carpal kinematics differ between stiffer wrists and wrists with higher laxity. Wrist laxity was quantified using a goniometer in ten subjects by measuring passive wrist flexion-extension (FE) range of motion (ROM). In vivo kinematics of subjects' scaphoid and lunate with respect to the radius were computed from computed tomography (CT) volume images in wrist radial and ulnar deviation positions. Scaphoid and lunate motion was defined as "column-type" if the bones flexed and extended during wrist radial-ulnar deviation (RUD), and "row-type" if the bones radial-ulnar deviated during wrist RUD. We found that through wrist RUD, the scaphoid primarily flexed and extended, but the scaphoids of subjects with decreased laxity had a larger component of RUD (R2 = 0.48, P < 0.05). We also determined that the posture of the scaphoid in the neutral wrist position predicts wrist radial deviation (RD) ROM (R2 = 0.46, P < 0.05). These results suggest that ligament laxity plays a role in affecting carpal bone motion of the proximal row throughout radial and ulnar deviation motions; however, other factors such as bone position may also affect motion. By developing a better understanding of normal carpal kinematics and how they are affected, this will help physicians provide patient-specific approaches to different wrist pathologies.

Stabilization of scaphoid type B2 fractures with one or two headless compression screws

INTRODUCTION

Fractures of the scaphoid account for the most commonly injured carpal bone. Minimally displaced fractures of the waist will heal in 85-90% when using a below elbow cast. However, fractures with displacement have a higher risk for nonunion. Therefore, open reduction and fixation with headless compression screws (HCS) have become the preferred method of treatment. The aim of this study was to compare the radiological and clinical outcome of unstable scaphoid B2 type fractures, stabilized using one or two headless compression screws.

PATIENTS AND METHODS

A total of 47 unstable scaphoid B2 type fractures were included in this retrospective follow-up study. Twelve patients were not accessable and three refused to attend follow-up checks. Therefore, a total of 32 patients were included in this study with a mean follow-up interval of 43 (12-81) months. Twenty-two patients were treated using one HCS and ten with two HCS. Clinical assessment included range of motion (ROM), pain according to the visual analogue scale (VAS), grip strength, Disability of the Arm, Shoulder and Hand Score, Patient-Rated Wrist Evaluation Score, Michigan Hand Outcomes Questionnaire and modified Green O'Brien Wrist Score. The follow-up study on each patient included a CT-Scan of the wrist which was analyzed for union, osteoarthritis, dorsiflexed intercalated segment instability and humpback deformity.

RESULTS

Radiologically, 29/32 (91%) of the scaphoid B2 type fractures showed union, 10/10 (100%) in the two HCS group and 19/22 (86%) in the one HCS group (p < 0.05). No significant differences could be found in respect to ROM, grip strength, VAS and scores between the groups. Screw removal was necessary in two patients in the two HCS group and one in the one HCS group.

CONCLUSION

The unstable B2 type fractures of the scaphoid, when using two HCS without bone grafting is a safe method, shows a significantly higher union rate and equal clinical outcome compared to stabilization using only one HCS.

Scapholunate Interosseous Ligament Anatomy and Biomechanics

Injury to the scapholunate interosseous ligament is one of the most common causes of carpal instability and can impart considerable compromise to the patient's hand function. However, the management of scapholunate ligament injuries remains a dynamic concept, especially with regard to the multitude of options and techniques that exist for its surgical treatment. We present a thorough review of scapholunate anatomy and morphology, and the role of the scapholunate articulations in the kinetics and pathomechanics of wrist instability. We also review the current literature on the biomechanical properties of the scapholunate ligament and its subcomponents. A sound understanding of the anatomy and biomechanics of the scapholunate ligament can clarify its instability and may better orient current reconstructive procedures or pioneer better future techniques.

Cadaveric scapholunate reconstruction using the ligament augmentation and reconstruction system

Background Untreated scapholunate ligament disruption may lead to progressive wrist arthritis. Current techniques used to treat the disruption may not prevent arthritis because of attenuation of a reconstructive ligament substitute or failure to re-establish normal wrist kinematics. Questions/Purposes This study evaluates a combined synthetic-autologous technique for the treatment of scapholunate dissociation. Methods Scapholunate dissociation was created in six cadaveric wrists. The dorsal and volar components of the scapholunate ligament were reconstructed using the Ligament Augmentation & Reconstruction System (LARS; LARS, Arc-sur-Tille, France) and a modified Blatt capsulodesis performed. Reconstructed wrists were subjected to cyclic passive motion. Outcomes were measured radiologically and compared using Student's t-test. Results Carpal alignment was re-established following scapholunate ligament reconstruction. Carpal alignment was maintained after cyclic loading. Conclusions The technique described corrected the carpal malalignment associated with scapholunate dissociation. Corrected positions were maintained after one thousand cycles of flexion and extension without fraying or loosening of the LARS. Clinical Relevance Current popular techniques for scapholunate reconstruction do not address the important dorsal and palmar components of the ligament that control their intercarpal motion. Reconstruction of the dorsal and palmar components of the scapholunate ligament can be achieved through a dorsal approach to the wrist.

Scaphoid nonunions treated with 2 headless compression screws and bone grafting

PURPOSE

To evaluate union and complication rates associated with the use of 2 headless compression screws and bone grafting for the treatment of scaphoid nonunions.

METHODS

A total of 19 patients (18 male and 1 female) at an average age of 21 years were treated with open reduction and internal fixation with 2 cannulated, headless, compression screws for scaphoid nonunions. Bone grafting techniques included corticocancellous autograft from the iliac crest in 14 patients, capsular-based vascularized distal radius graft in 3, and medial femoral condyle free vascularized bone graft in 2. Patients were treated an average 19 months after the injury. Fracture nonunions were at the waist (n = 12), proximal third (n = 5), or distal third (n = 2) of the scaphoid. Dorsal (n = 7) and volar (n = 12) surgical approaches were used.

RESULTS

All fractures had clinical and radiographic evidence of bone union at an average of 3.6 months. Postoperative computed tomography scans were available in 13 patients and showed union without evidence of screw penetration of the scaphoid cortex. No complications occurred in this series, and no revision procedures have been necessary.

CONCLUSIONS

Our results indicate that the use of 2 headless compression screws for the treatment of scaphoid nonunions is safe and effective. A variety of bone grafting techniques can be used with this technique. The use of 2 compression screws may provide superior biomechanical stability and ultimately improve outcomes measured with future long-term comparative studies.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

In vivo length changes of wrist ligaments at full wrist extension

The aim of this study was to investigate the length changes of carpal ligaments when loaded in full extension in vivo. We obtained computed tomography scans of the right wrists in three positions for six volunteers: neutral; 75° extension; and 75° extension with a further 10° of radial deviation. Nine ligaments were measured and analysed with computer modelling. The results showed that the radioscaphocapitate, long radiolunate, and ulnolunate ligaments lengthened the most at full wrist extension, suggesting that they were under greatest load. The radioscapholunate, ulnocapitate, and ulnotriquetral ligaments lengthened further with the addition of wrist radial deviation. At full extension, the dorsal intercarpal ligament inserting on the scaphoid was lengthened. The dorsal radiocarpal and dorsal intercarpal ligaments inserting on the trapezoid were shortened, suggesting reduced loading. In conclusion, a number of volar carpal ligaments lengthened significantly in full wrist extension and the ulnar carpal ligaments were further lengthened at wrist radial deviation.

In vivo changes in contact regions of the radiocarpal joint during wrist hyperextension

PURPOSE

Distal radius and scaphoid fractures commonly occur after a fall with the hand outstretched and wrist hyperextended. We investigated contact characteristics of the radiocarpal joint in neutral position, hyperextension, and hyperextension combined with radial deviation in vivo.

METHODS

Eight volunteers without a known history of wrist injury were enrolled. We obtained computed tomography scans with 3-dimensional reconstructions of the subjects' right wrists in neutral, hyperextension, and hyperextension with 10° of radial deviation. The contact regions of the radiocarpal joint were mapped. The direction and distance of changes in the contact region centers were recorded and analyzed.

RESULTS

From neutral position to hyperextension, the contact of the scaphoid substantially shifted from the middle to the dorsal part of the articular surface of the radius in 5 of the 8 wrists. With these wrists further deviated radially, the contact shifted to the surface over the radial styloid. In the other wrists, the contact of the scaphoid remained in the center of the radial articular surface. In all wrists, the contact of the radius on the scaphoid shifted from the proximal lateral surface of the scaphoid to the proximal dorsal surface of the scaphoid, and the contact of the radius on the lunate shifted dorsally.

CONCLUSIONS

During wrist hyperextension, the contact of the scaphoid on the distal radius exhibited 2 possible types of changes: either shifting from the mid-portion to the dorsal ridge of the articular surface of the radius or remaining at the center of the articular surface. Combined wrist hyperextension with radial deviation caused the scaphoid to contact the radius over the radial styloid. The contact of the radius on the scaphoid shifted from proximal lateral to proximal dorsal scaphoid, and that on the lunate shifted dorsally.

CLINICAL RELEVANCE

This study provided in vivo mechanical findings to improve our understanding of the mechanism of hyperextension injuries of carpus.

[Relationship between midcarpal inclination angle and scaphoid kinematic]

OBJECTIVE

To investigate if there is a correlation between the so-called midcarpal inclination angle and the kinematic behavior of the scaphoid.

PATIENTS AND METHODS

The population studied was 60 patients with postero-anterior radiographs of the wrist in full radial and ulnar deviation. Each patient was assessed for the type of lunate by two independent observers. For each pair of radiographs the Midcarpal Inclination Angle and the Scaphoid Flexion Index (SFI) was determined.

RESULTS

Twenty-three cases were classified as lunate type I, 19 cases as type II. The average midcarpal inclination angle was 55.2° (SD±6.1) for wrists with a lunate type I and 63.8° (DE±6.3) for type II (p<0.0001). There was a significant linear relationship between the midcarpal inclination angle and the Scaphoid Flexion Index (p=0.02).

CONCLUSIONS

The wrists with a midcarpal inclination angle greater than 60° (type II lunate) had a scaphoid rotating according to a "columnar pattern", during radioulnar inclinations (predominant rotation along the sagittal plane), while the wrists with a lunate type I behave according to a "row pattern".

In vivo length and changes of ligaments stabilizing the thumb carpometacarpal joint

PURPOSE

To investigate the lengths and changes of selected ligaments stabilizing the thumb carpometacarpal (CMC) joint during thumb motion in vivo.

METHODS

We obtained serial computed tomography scans of the thumb CMC joints of 6 healthy volunteers during thumb flexion, abduction, and opposition. We reconstructed the 3-dimensional structures of the bones of the thumb CMC joint using customized software and modeled the paths of fibers of 5 principal ligaments--deep anterior oblique (beak), dorsoradial, posterior oblique, intermetacarpal, and dorsal intermetacarpal--at each of the CMC joint positions studied. We estimated the virtual lengths of these ligaments in neutral position, flexion, abduction, and opposition of the CMC joint by measuring the distances between the origin and the insertion of individual ligaments, and statistically analyzed the length changes.

RESULTS

The estimated length of the CMC joint ligaments underwent significant changes during thumb motion in vivo. Thumb flexion led to the greatest changes in ligament lengths. During flexion, all the ligaments lengthened significantly (p < .05 or p < .01), except for the beak ligament, which shortened significantly (p < .001). The lengths of the ligaments changed similarly during thumb abduction and opposition, except for the dorsoradial ligament. In both motions, the posterior oblique and dorsal intermetacarpal ligaments lengthened and the beak ligament shortened significantly (p < .05 or p < .01). During the 3 thumb motions, the beak ligament underwent marked shortening, while the other measured ligaments lengthened to varied extent.

CONCLUSIONS

The estimated lengths of principal ligaments stabilizing the CMC joint change substantially during thumb motions in vivo. Thumb flexion causes the greatest changes of the ligament lengths; abduction and opposition result in similar changes in the ligament lengths. The beak ligaments shorten while the other ligaments lengthen. This in vivo study suggests that thumb motions expose the CMC joint ligaments to different tensions at these thumb positions, and that the ligaments are under lower tension during thumb opposition and abduction than during flexion.

In vivo length changes of carpal ligaments of the wrist during dart-throwing motion

PURPOSE

The dart-throwing motion is an important movement pattern during most wrist actions. The aim of this study was to investigate length changes in the wrist ligaments in different positions of the dart-throw motion in vivo.

METHODS

We obtained computed tomography scans of the wrists of 6 volunteers at 5 positions of the wrist during the dart-throw motion: 20° of radial deviation with 60° of extension; 10° of radial deviation with 30° of extension; the neutral position of the carpus; 20° of ulnar deviation with 30° of flexion; and 40° of ulnar deviation with 60° of flexion. We reconstructed the 3-dimensional carpal and distal radioulnar joint structures with customized software and computed changes in length of 8 palmar and dorsal wrist ligaments.

RESULTS

From wrist radial deviation with extension to ulnar deviation with flexion, the radioscaphocapitate, long radiolunate, ulnocapitate, and ulnotriquetral ligaments decreased significantly in length but the dorsal radiocarpal ligament and the dorsal intercarpal (DIC) ligament inserting on the trapezoid lengthened significantly; the ulnolunate ligament and the DIC ligament inserting on the scaphoid were shortest in neutral position.

CONCLUSIONS

At wrist radial extension, the radioscaphocapitate, long radiolunate, ulnocapitate, and ulnotriquetral ligaments are lengthened and under increased tension. At wrist ulnar flexion, the dorsal radiocarpal ligament and the DIC ligament inserting on the trapezoid are lengthened and under increased tension. The ulnolunate ligament and the DIC ligament inserting on the scaphoid are the shortest and under the least tension in neutral position. These findings will help us understand the biomechanics of the carpus during the dart-throwing motion.

Scaphoid and lunate movement in different ranges of carpal radioulnar deviation

PURPOSE

We aimed to investigate scaphoid and lunate movement in radial deviation and in slight and moderate ulnar deviation ranges in vivo.

METHODS

We obtained computed tomography scans of the right wrists from 20° radial deviation to 40° ulnar deviation in 20° increments in 6 volunteers. The 3-dimensional bony structures of the wrist, including the distal radius and ulna, were reconstructed with customized software. The changes in position of the scaphoid and lunate along flexion-extension motion (FEM), radioulnar deviation (RUD), and supination-pronation axes in 3 parts--radial deviation and slight and moderate ulnar deviation--of the carpal RUD were calculated and analyzed.

RESULTS

During carpal RUD, scaphoid and lunate motion along 3 axes--FEM, RUD, and supination-pronation--were the greatest in the middle third of the measured RUD (from neutral position to 20° ulnar deviation) and the smallest in radial deviation. Scaphoid motion along the FEM, RUD, and supination-pronation axes in the middle third was about half that in the entire motion range. In the middle motion range, lunate movement along the FEM and RUD axes was also the greatest.

CONCLUSIONS

During carpal RUD, the greatest scaphoid and lunate movement occurs in the middle of the arc--slight ulnar deviation--which the wrist frequently adopts to accomplish major hand actions. At radial deviation, scaphoid and lunate motion is the smallest.

Scaphoid kinematics before and after scaphotrapeziotrapezoidal ligament section. Assessment by radiostereometric analysis and computed tomography in a cadaver study

The purpose of this study was to measure changes in scaphoid kinematics after division of scaphotrapeziotrapezoidal ligaments, with the intention of determining a clinical measure that could be detected by computed tomography. Twelve freshly frozen cadaver upper extremities were marked with tantalum beads and fixed in positions of neutral, 30° extension, and 40° ulnar deviation. Stereoradiographs for bone migration analysis by radiostereometric analysis and computed tomography scans for visible assessment were obtained before and after scaphotrapeziotrapezoidal ligament section. After ligament resection there was a scaphoid supination of 5° and a small (less than 1 mm) radial, distal, and dorsal translation of the distal pole in 30° of wrist extension. In computed tomography reconstructions, the ligament section appeared as a 1 to 2 mm gap in the scaphotrapeziotrapezoidal corner, with loss of articulation between the distal scaphoid pole and the trapezoid bone and increased scaphoid flexion.

Studying primate carpal kinematics in three dimensions using a computed-tomography-based markerless registration method

The functional morphology of the wrist pertains to a number of important questions in primate evolutionary biology, including that of hominins. Reconstructing locomotor and manipulative capabilities of the wrist in extinct species requires a detailed understanding of wrist biomechanics in extant primates and the relationship between carpal form and function. The kinematics of carpal movement, and the role individual joints play in providing mobility and stability of the wrist, is central to such efforts. However, there have been few detailed biomechanical studies of the nonhuman primate wrist. This is largely because of the complexity of wrist morphology and the considerable technical challenges involved in tracking the movements of the many small bones that compose the carpus. The purpose of this article is to introduce and outline a method adapted from human clinical studies of three-dimensional (3D) carpal kinematics for use in a comparative context. The method employs computed tomography of primate cadaver forelimbs in increments throughout the wrist's range of motion, coupled with markerless registration of 3D polygon models based on inertial properties of each bone. The 3D kinematic principles involved in extracting motion axis parameters that describe bone movement are reviewed. In addition, a set of anatomically based coordinate systems embedded in the radius, capitate, hamate, lunate, and scaphoid is presented for the benefit of other primate functional morphologists interested in studying carpal kinematics. Finally, a brief demonstration of how the application of these methods can elucidate the mechanics of the wrist in primates illustrates the closer-packing of carpals in chimpanzees than in orangutans, which may help to stabilize the midcarpus and produce a more rigid wrist beneficial for efficient hand posturing during knuckle-walking locomotion.

The advantage of throwing the first stone: how understanding the evolutionary demands of Homo sapiens is helping us understand carpal motion

Unlike any other diarthrodial joint in the human body, the "wrist joint" is composed of numerous articulations between eight carpal bones, the distal radius, the distal ulna, and five metacarpal bones. The carpal bones articulate with each other as well as with the distal radius, distal ulna, and the metacarpal bases. Multiple theories explaining intercarpal motion have been proposed; however, controversy exists concerning the degree and direction of motion of the individual carpal bones within the two carpal rows during different planes of motion. Recent investigations have suggested that traditional explanations of carpal bone motion may not entirely account for carpal motion in all planes. Better understanding of the complexities of carpal motion through the use of advanced imaging techniques and simultaneous appreciation of human anatomic and functional evolution have led to the hypothesis that the "dart thrower's motion" of the wrist is uniquely human. Carpal kinematic research and current developments in both orthopaedic surgery and anthropology underscore the importance of the dart thrower's motion in human functional activities and the clinical implications of these concepts for orthopaedic surgery and rehabilitation.

In vivo length changes of selected carpal ligaments during wrist radioulnar deviation

PURPOSE

To investigate changes in the lengths of selected carpal ligaments during wrist radioulnar deviation in vivo.

METHODS

We studied in vivo changes in the lengths of fibers of 5 palmar and dorsal intracapsular ligaments of the wrist during radioulnar deviation in 6 wrists of healthy volunteers using a noninvasive approach. Using serial computed tomography scans and volume registration techniques, the carpal kinematics were examined at 4 positions, from 40 degrees ulnar deviation to 20 degrees radial deviation, in 20 degrees increments. The 3-dimensional structures of the carpal bones, distal radius and ulna, and metacarpal bones were reconstructed using customized software. We modeled the paths of fibers of 5 palmar and dorsal carpal ligaments: radioscaphocapitate (RSC), long radiolunate (LRL), ulnocapitate (UC), dorsal intercarpal (DIC), and dorsal radiocarpal (DRC) ligaments. We analyzed changes in the lengths of these ligaments during wrist radioulnar deviation.

RESULTS

During wrist ulnar deviation, the RSC, LRL, and DIC ligaments lengthened significantly. During radial deviation, the UC and DRC ligaments lengthened significantly. Compared with their lengths at the neutral position of the carpus, the LRL ligament showed the greatest elongation rate at wrist ulnar deviation, and the DRC ligament showed the greatest elongation rate at wrist radial deviation among the 5 ligaments studied.

CONCLUSIONS

Among ligaments measured, the RSC, LRL, and DIC ligaments are tensed during wrist ulnar deviation. The UC and DRC ligaments are tensed during wrist radial deviation. Results of this in vivo study suggest that radial or ulnar deviation may predispose some carpal ligaments to excessive tensile load. The finding that the ligaments undergo different elongation rates during wrist motion may also indicate their roles in maintaining normal wrist kinematics.

In vivo changes in lengths of the ligaments stabilizing the distal radioulnar joint

PURPOSE

To investigate changes in lengths of the ligaments stabilizing the distal radioulnar joint during forearm pronation and supination in vivo.

METHODS

We studied in vivo kinematics of the distal radioulnar joint by measuring the length changes of the ligaments of the distal radioulnar joint in 6 wrists of normal volunteers. Using serial computed tomography scans and volume registration techniques, the distal radioulnar joints were examined at 7 positions from 90 degrees pronation to 90 degrees supination in 30 degrees increments. The 3-dimensional structures of the joint were reconstructed with customized software. The paths of palmar and dorsal superficial and deep fibers of the radioulnar ligaments were modeled, and changes in their lengths were computed and analyzed statistically.

RESULTS

The lengths of the palmar superficial radioulnar ligaments decreased significantly during forearm pronation from 90 degrees to 30 degrees compared with those at the other positions. During pronation from 90 degrees to neutral rotation, lengths of the dorsal deep radioulnar ligaments decreased significantly. The lengths of the dorsal superficial radioulnar ligament decreased significantly during forearm supination from neutral rotation to 90 degrees , as did the lengths of the palmar deep radioulnar ligaments. The palmar and dorsal superficial radioulnar ligaments showed greater length changes than did the palmar and dorsal deep radioulnar ligaments during forearm pronation-supination. The dorsal superficial radioulnar ligament had the greatest length changes during pronation-supination among the studied ligaments.

CONCLUSIONS

These in vivo measurements validate that in forearm pronation, the dorsal superficial radioulnar ligament and palmar deep radioulnar ligament tighten, serving as restraints for the distal radioulnar joint instability. In forearm supination, the palmar superficial radioulnar ligament and dorsal deep radioulnar ligament tighten, maintaining stability of the distal radioulnar joint.

Management of wrist injuries

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the anatomy and the biomechanical properties of the wrist. 2. Understand the standard examination process for wrist injuries. 3. Accurately diagnose common wrist conditions. 4. Establish a management plan for wrist problems.

BACKGROUND

Although common, wrist injuries and conditions are difficult to treat if the physician is unfamiliar with their management.

METHODS

Wrist anatomy and kinematics are discussed. Physical and radiographic examinations that are mandatory for diagnosing wrist conditions are presented. Common wrist injuries are reviewed.

RESULTS

Understanding the anatomy and kinematics of the wrist is important in diagnosing and treating wrist conditions and in predicting outcomes after treatment. Physical examination of the wrist requires an understanding of the surface anatomy and a number of specific maneuvers. Physicians should also be familiar with other diagnostic tests, which include radiography, arthrography, computed tomography, magnetic resonance imaging, and arthroscopy.

CONCLUSIONS

Physicians who treat wrist injuries should be able to establish an adequate management plan for common wrist injuries and conditions and be able to predict outcomes based on these treatment plans.

Influence of lunate type on scaphoid kinematics

PURPOSE

To assess the influence of lunate type on scaphoid kinematics.

METHODS

One hundred normal wrists had fluoroscopic assessment of the wrist in maximal radial, neutral, and ulnar deviation. The shortest distance in a neutral position between the capitate and triquetrum, C-T distance, determined lunate type. A type I lunate had a C-T distance of < or =2 mm, a type II lunate > or =4 mm, and an intermediate group lay between these values. Scaphoid flexion and translation in radial and ulna deviation was measured.

RESULTS

There were 18 subjects with a type I lunate, 19 with an intermediate lunate, and 63 with a type II lunate. There was no statistically significant difference between lunate type, subject age, or hand dominance. There was a statistically significant higher proportion of women with a type I lunate. Subjects with a type II lunate had a statistically greater amount of flexion during radioulnar deviation as determined by CR index (0.79 vs 0.91) and scaphoid flexion index (0.21 vs 0.09). Subjects with a type II lunate had statistically less translation during radioulnar deviation as determined by translation ratio (0.22 vs 0.31) and scaphoid inclination index (0.18 vs 0.23). The average scaphoid kinematic index in subjects with a type II lunate was 1.24, intermediate 0.86, and type I 0.42. A scaphoid kinematic index of greater than 1 indicates the scaphoid has more flexion during radioulnar deviation than translation.

CONCLUSIONS

Wrists with a type I lunate show statistically greater scaphoid translation with radial deviation. Wrists with a type II lunate show statistically greater scaphoid flexion with radial deviation. Intermediate lunates have intermediate scaphoid mechanics. This allows the surgeon to determine the likely wrist scaphoid mechanics based on the lunate type determined from a single posterior-anterior x-ray.

Carpal kinematics after proximal row carpectomy

PURPOSE

Proximal row carpectomy (PRC) is a clinically useful motion-sparing procedure for the treatment of certain degenerative conditions of the wrist. Clinical outcome studies after PRC have shown that wrist flexion-extension averages approximately 60% of that of the contralateral wrist. The purpose of this study was to determine how the kinematics of the wrist are altered after PRC.

METHODS

Eight fresh-frozen cadaver forearms were scanned with computed tomography before and after PRC. Forearms were scanned in 5 different wrist positions (neutral, extension, flexion, radial deviations, and ulnar deviation). Wrists were positioned dynamically and then held statically in a custom fixture through forces applied to the 4 wrist flexor/extensor tendon groups. Three-dimensional computer models of the radius, lunate, and capitate were generated from the computed tomographic images, and the kinematics of the capitate and lunate were calculated relative to the neutral position. For the intact wrist, the motion of the capitate was calculated relative to both the lunate (midcarpal motion) and the radius (overall wrist motion) and the motion of the lunate was calculated relative to the radius (radiocarpal motion). After PRC, only the movement of the capitate relative to the radius was calculated, which represents radiocapitate and overall wrist motion. All motions were plotted in 3 dimensions for purposes of qualitative visualization.

RESULTS

After PRC, the capitate articulated with the lunate fossa of the radius for all positions in all samples. Overall wrist motion decreased 28%, 30%, 40%, and 12% in flexion, extension, radial deviation, and ulnar deviation, respectively. Motion at the radiocarpal joint after PRC, however, was greater compared with motion at the radiocarpal and midcarpal joints of the intact wrist during flexion and extension. This was not the case in radial deviation because of impingement of the trapezoid on the radial styloid. In radial and ulnar deviation, motion of the capitate head changed from predominantly rotational in the intact wrist (midcarpal joint) to a combination of rotation and translation after PRC (radiocarpal joint).

CONCLUSIONS

Removal of the proximal carpal row decreased normal wrist flexion and extension. Although ulnar deviation was preserved, radial deviation was limited by impingement of the trapezoid on the radial styloid. Radiocapitate range of motion after PRC was greater than capitolunate range of motion in the intact wrists. Compared with previously published requirements, wrist range of motion observed after PRC was sufficient for activities of daily living.

Carpal kinematics

The motion of the eight carpal bones is extremely complex, and their accurate measurement has been hampered by their multiplanar rotations and translations, the irregularity of their shape, and the small magnitudes of movements. However, an accurate three-dimensional understanding of carpal motion is critical for academic and clinical purposes, and may play an important role in assessing surgical procedures or rehabilitation protocols.

Kinematics of the midcarpal and radiocarpal joint in flexion and extension: an in vitro study

PURPOSE

To apply carpal kinematic analysis using noninvasive medical imaging to investigate the midcarpal and radiocarpal contributions to wrist flexion and extension in a quasidynamic in vitro model.

METHODS

Eight fresh-frozen cadaver wrists were scanned with computed tomography in neutral, full flexion, and full extension. Body-mass-based local coordinate systems were used to track motion of the capitate, lunate, and scaphoid with the radius as a fixed reference. Helical axis motion parameters and Euler angles were calculated for flexion and extension.

RESULTS

Minimal out-of-plane carpal motion was noted with the exception of small amounts of ulnar deviation and supination in flexion. Overall wrist flexion was 68 degrees +/- 12 degrees and extension was 50 degrees +/- 12 degrees. In flexion, 75% of wrist motion occurred at the radioscaphoid joint, and 50% occurred at the radiolunate joint. In extension, 92% of wrist motion occurred at the radioscaphoid joint, and 52% occurred at the radiolunate joint. Midcarpal flexion/extension between the capitate and scaphoid was 0 degrees +/- 5 degrees in extension and 10 degrees +/- 13 degrees in flexion. Midcarpal flexion/extension between the capitate and lunate was larger, with 15 degrees +/- 11 degrees in extension and 22 degrees +/- 19 degrees in flexion.

CONCLUSIONS

The capitate and scaphoid tend to move together. This results in greater flexion/extension for the scaphoid than the lunate at the radiocarpal joint. The lunate has greater midcarpal motion between it and the capitate than the scaphoid does with the capitate. The engagement between the scaphoid and capitate is particularly evident during wrist extension. Out-of-plane motion was primarily ulnar deviation at the radiocarpal joint during flexion. These results are clinically useful in understanding the consequences of isolated fusions in the treatment of wrist instability.

An anatomic study of the triquetrum-hamate joint

PURPOSE

To investigate the articulating surface of the triquetrum-hamate joint (TqH).

METHODS

The carpal bones of 46 wrist specimens were examined. The shape of the TqH joint surfaces were investigated, with focus on variations in the shape of the hamate and corresponding triquetrum and the presence and position of convex and concave surfaces.

RESULTS

Two distinct patterns of hamate TqH articular surfaces were identified, designated type I (31 of 46) and type II (15 of 46). The triquetral TqH articular surface also was found to have 2 distinct patterns, designated type A (18 of 46) and type B (15 of 46). Of the triquetrums examined 13 of 46 had characteristics that were a variable mixture of the 2 identifiable triquetral surface types, but these did not have sufficient similarity to constitute a third triquetrum surface type. The corresponding articulation patterns of these joint surfaces showed a strong trend for a type A triquetrum to articulate with a type I hamate (18 of 46 of all joints) and for a type B triquetrum to articulate with a type II hamate (13 of 46 of all joints). No association was seen between lunate types and type I or type II hamates.

CONCLUSIONS

These findings suggest the existence of 2 distinct TqH joint patterns, which have been termed TqH-1 and TqH-2. There appears to be a spectrum of variation between these 2 identifiable types. As a result, the TqH is best described as a spectrum, with TqH-1 at one end and TqH-2 at the other. A TqH-1 joint is a helicoidal configuration. It is double-faceted, with the hamate and the triquetrum articular surfaces possessing complementary concave and convex parts. A TqH-2 joint has a predominantly oval convex shape, whereas the primarily concave triquetrum is better described as a dish for the flatter hamate. It has no hamate groove or distal ridge.

Coordinate systems for the carpal bones of the wrist

The eight small and complexly shaped carpal bones of the wrist articulate in six degrees of freedom with each other and to some extent with the radius and the metacarpals. With the increasing number and sophistication of studies of the carpus, a standardized definition for a coordinate system for each the carpal bones would aid in the reporting and comparison of findings. This paper presents a method for defining and constructing a coordinate system specific to each of the eight carpal bones based upon the inertial properties of the bone, derived from surface models constructed from three-dimensional (3-D) medical image volumes. Surface models from both wrists of 5 male and 5 female subjects were generated from CT image volumes in two neutral wrist positions (functional and clinical). An automated algorithm found the principal inertial axes and oriented them according to preset conditions in 85% of the bones, the remaining bones were corrected manually. Six of the eight carpal bones were significantly more extended in the functional neutral position than in the clinical neutral position. Gender had no significant effect on carpal bone posture in either wrist position. Correlations between the 3-D carpal posture and the commonly used 2-D clinical radiographic carpal angles are established. 3-D coordinate systems defined by the anatomy of the carpal bone, such as the ones presented here, are necessary to completely describe 3-D changes in the posture of the carpal bones.

A kinematic model of the wrist based on maximization of joint contact area

The wrist is a complex joint and the factors governing its behaviour are poorly understood. A hypothesis that the movement of the carpal bones could be predicted using a minimum energy principle was tested. Carpal bones were dissected from a cadaveric forearm and their shapes were laser-digitized to obtain three-dimensional computer models. A computer program was created to measure contact area between neighbouring articular surfaces and to maximize this quantity by adjusting the six degrees of freedom of the bone models. This procedure was performed for 1.0° increments of rotation applied to the capitate bone up to 20° of ulnar and 10° of radial deviation. The model correctly predicted certain aspects of the complex behaviour of the carpal bones. The results for the scaphoid in particular displayed characteristics in common with known behaviour of this bone. During 20° of unlar deviation and 10° of radial deviation, the bone demonstrated 11.3° of extension and 9.4° of flexion respectively. The novelty of the study lay in the fact that the model did not rely upon ligamentous constraints. The results are encouraging, considering the only information used by the algorithm was the shape of the articular surfaces.

In vivo radiocarpal kinematics and the dart thrower's motion

BACKGROUND

Wrist motion is dependent on the complex articulations of the scaphoid and lunate at the radiocarpal joint. However, much of what is known about the radiocarpal joint is limited to the anatomically defined motions of flexion, extension, radial deviation, and ulnar deviation. The purpose of the present study was to determine the three-dimensional in vivo kinematics of the scaphoid and lunate throughout the entire range of wrist motion, with special focus on the dart thrower's wrist motion, from radial extension to ulnar flexion.

METHODS

The three-dimensional kinematics of the capitate, scaphoid, and lunate were calculated from serial computed tomography scans of both wrists of fourteen healthy male subjects (average age, 25.6 years; range, twenty-two to thirty-four years) and fourteen healthy female subjects (average age, 23.6 years; range, twenty-one to twenty-eight years), which yielded data on a total of 504 distinct wrist positions.

RESULTS

The scaphoid and lunate primarily flexed or extended in all directions of wrist motion, and their rotation varied linearly with the direction of wrist motion (R2= 0.90 and 0.82, respectively). Scaphoid and lunate motion was significantly less along the path of the dart thrower's motion than in any other direction of wrist motion (p < 0.01 for both carpal bones). The scaphoid and lunate translated radially (2 to 4 mm) when extended, but they did not translate appreciably when flexed.

CONCLUSIONS

The dart thrower's path defined the transition between flexion and extension rotation of the scaphoid and lunate, and it identified wrist positions at which scaphoid and lunate motion approached zero. These findings indicate that this path of wrist motion confers a unique degree of radiocarpal stability and suggests that this direction, rather than the anatomical directions of wrist flexion-extension and radioulnar deviation, is the primary functional direction of the radiocarpal joint.

In vivo radiocarpal kinematics and the dart thrower's motion

BACKGROUND

Wrist motion is dependent on the complex articulations of the scaphoid and lunate at the radiocarpal joint. However, much of what is known about the radiocarpal joint is limited to the anatomically defined motions of flexion, extension, radial deviation, and ulnar deviation. The purpose of the present study was to determine the three-dimensional in vivo kinematics of the scaphoid and lunate throughout the entire range of wrist motion, with special focus on the dart thrower's wrist motion, from radial extension to ulnar flexion.

METHODS

The three-dimensional kinematics of the capitate, scaphoid, and lunate were calculated from serial computed tomography scans of both wrists of fourteen healthy male subjects (average age, 25.6 years; range, twenty-two to thirty-four years) and fourteen healthy female subjects (average age, 23.6 years; range, twenty-one to twenty-eight years), which yielded data on a total of 504 distinct wrist positions.

RESULTS

The scaphoid and lunate primarily flexed or extended in all directions of wrist motion, and their rotation varied linearly with the direction of wrist motion (R2= 0.90 and 0.82, respectively). Scaphoid and lunate motion was significantly less along the path of the dart thrower's motion than in any other direction of wrist motion (p < 0.01 for both carpal bones). The scaphoid and lunate translated radially (2 to 4 mm) when extended, but they did not translate appreciably when flexed.

CONCLUSIONS

The dart thrower's path defined the transition between flexion and extension rotation of the scaphoid and lunate, and it identified wrist positions at which scaphoid and lunate motion approached zero. These findings indicate that this path of wrist motion confers a unique degree of radiocarpal stability and suggests that this direction, rather than the anatomical directions of wrist flexion-extension and radioulnar deviation, is the primary functional direction of the radiocarpal joint.

Kinematics of the midcarpal and radiocarpal joints in radioulnar deviation: an in vitro study

PURPOSE

Carpal kinematics have been studied widely yet remain difficult to understand fully. The noninvasive measurement of carpal kinematics through medical imaging has become popular. Studies have shown that with radial deviation the scaphoid and lunate flex whereas the capitate moves radiodorsally relative to the lunate. This study investigated the midcarpal and radiocarpal contributions to radial and ulnar deviation of the wrist. This was accomplished through noninvasive characterization of the scaphoid, lunate, and capitate using 3-dimensional medical imaging of the wrist in radial and ulnar deviation.

METHODS

Eight fresh-frozen and thawed cadaveric wrists were used in an experimental set-up that positioned the wrist through spring-scale actuation of the 4 wrist flexor and extensor tendon groups. The wrists were scanned by computed tomography in neutral and full radial and ulnar deviation. Body mass-based local coordinate systems were used to track the motion of the capitate, lunate, and scaphoid with the radius as a fixed reference. Helical axis motion and Euler angles were calculated from neutral to radial and ulnar deviation for the capitate relative to the radius, lunate, and scaphoid and for the lunate and scaphoid relative to the radius.

RESULTS

The capitate, scaphoid, and lunate moved in a characteristic manner relative to the radius and to one another. Radial and ulnar deviation occurred primarily in the midcarpal joint. Midcarpal motion accounted for 60% of radial deviation and 86% of ulnar deviation. In radial deviation the proximal row flexed and the capitate extended; the converse was true in ulnar deviation.

CONCLUSIONS

Radioulnar deviation (in-plane motion) occurred mostly through the midcarpal joint, with a lesser contribution from the radiocarpal joint. The results of our study agree with previous investigations that found the scaphoid and lunate flex in radial deviation (out-of-plane motion) relative to the radius whereas the capitate extends (out-of-plane motion) relative to the scaphoid/lunate (with the converse occurring in ulnar deviation). Our study shows how these out-of-plane motions combine to produce in-plane wrist radioulnar deviation. The use of 3-dimensional visualization greatly aids in the understanding of these motions. The results of our study may be useful clinically in understanding the consequences of isolated midcarpal fusions in the treatment of wrist instability.

Development and Validation of a Computed Tomography-Based Methodology to Measure Carpal Kinematics

Motion of the wrist bones is complicated and difficult to measure. Noninvasive measurement of carpal kinematics using medical images has become popular. This technique is difficult and most investigators employ custom software. The objective of this paper is to describe a validated methodology for measuring carpal kinematics from computed tomography (CT) scans using commercial software. Four cadaveric wrists were CT imaged in neutral, full flexion, and full extension. A registration block was attached to the distal radius and used to align the data sets from each position. From the CT data, triangulated surface models of the radius, lunate, and capitate bones were generated using commercial software. The surface models from each wrist position were read into engineering design software that was used to calculate the centroid (position) and principal mass moments of inertia (orientation) of (1) the capitate and lunate relative to the fixed radius and (2) the capitate relative to the lunate. These data were used to calculate the helical axis kinematics for the motions from neutral to extension and neutral to flexion. The kinematics were plotted in three dimensions using a data visualization software package. The accuracy of the method was quantified in a separate set of experiments in which an isolated capitate bone was subjected to two different known rotation/translation motions for ten trials each. For comparison to in vivo techniques, the error in distal radius surface matching was determined using the block technique as a gold standard. The motion that the lunate and capitate underwent was half that of the overall wrist flexion-extension range of motion. Individually, the capitate relative to the lunate and the lunate relative to the radius generally flexed or extended about 30 deg, while the entire wrist (capitate relative to radius) typically flexed or extended about 60 deg. Helical axis translations were small, ranging from 0.6 mm to 1.8 mm across all motions. The accuracy of the method was found to be within 1.4 mm and 0.5 deg (95% confidence intervals). The mean error in distal radius surface matching was 2.4 mm and 1.2 deg compared to the use of a registration block. Carpal kinematics measured using the described methodology were accurate, reproducible, and similar to findings of previous investigators. The use of commercially available software should broaden the access of researchers interested in measuring carpal kinematics using medical imaging.

The triquetrum-hamate joint: an anatomic and in vivo three-dimensional kinematic study

PURPOSE

To obtain anatomic and kinematic information regarding the relative motion of the triquetrum-hamate (TqH) joint.

METHODS

In this anatomic study the contact surface constraints of the TqH joint that affect TqH motion were investigated by passively simulating TqH motion according to the kinematic data. Two fresh and 28 embalmed cadaver wrists were dissected. In the kinematic study we studied the in vivo 3-dimensional (3D) kinematics of the TqH joint during radioulnar deviation (RUD) and wrist flexion and extension motion (FEM) in 5 healthy wrists using a magnetic resonance image (MRI)-based markerless bone registration algorithm. Animations of the relative motion of the TqH joint were created and accurate estimates of the relative positions and orientations of the bones and axes of rotation of TqH motion during RUD and FEM were obtained.

RESULTS

The anatomic study revealed that the contact surface constraints of the TqH joint include primarily the oval convex surface of the hamate. In the kinematic study TqH motion was likely to be not helicoidal but rotational around an oval convex surface of the hamate. In RUD the triquetral movement was rotation in an ulnoflexion-radial extension plane of the wrist. In FEM it was rotation in an almost flexion-extension plane of the wrist. The axes of rotation of the TqH joint in all wrist motions always ran distal to the TqH joint.

CONCLUSIONS

Typical motion of the TqH joint in functional range of motion is not a helicoidal motion on the saddle, but rather a rotational motion on an oval, whose axes of rotation are located on the distal side of the joint.

In vivo analysis of carpal kinematics and comparative review of the literature

PURPOSE

Techniques have been developed very recently with which it is possible to quantify accurately in vivo 3-dimensional (3-D) carpal kinematics. The aim of this study was to evaluate the feasibility of our novel 3-D registration technique by comparing our data with data found in the literature.

METHOD

The right wrists of 11 healthy volunteers were imaged by spiral computed tomography (CT) during radial-ulnar deviation and 5 of those wrists were imaged also during flexion-extension motion. With a matching technique relative translations and rotations of the carpal bones were traced. We compared our in vivo results with data presented in the literature.

RESULTS

We found our in vivo data largely to concur with in vitro data presented in the literature. In vivo studies revealed only larger out-of-plane motions within the proximal carpal row than described in most in vitro studies. In vivo studies also showed larger interindividual variations.

CONCLUSIONS

A single functional model of carpal kinematics could not be determined. We expect that in vivo 3-D CT studies on carpal kinematics, especially when applied to dynamic wrist motion, will have future diagnostic applications and provide information on long-term results of surgical interventions.