The effect of anatomic landmark selection of the distal humerus on registration accuracy in computer-assisted elbow surgery

Morphometric Evaluation of Detailed Asymmetry for the Proximal Humerus in Korean Population

Computer-assisted orthopedic surgery and patient-specific instruments are widely used in orthopedic fields that utilize contralateral side bone data as a template to restore the affected side bone. The essential precondition for these techniques is that the left and right bone features are similar. Although proximal humerus fracture accounts for 4% to 8% of all fractures, the bilateral asymmetry of the proximal humerus is not fully understood. The aim of this study is to investigate anthropometric differences of the bilateral proximal humerus. One hundred one pairs of Korean humerus CT data from 51 females and 50 males were selected for this research. To investigate bilateral shape differences, we divided the proximal humerus into three regions and the proximal humerus further into five sections in each region. The distance from the centroid to the cortical outline at every 10 degrees was measured in each section. Differences were detected in all regions of the left and right proximal humerus; however, males had a larger number of significant differences than females. Large bilateral differences were measured in the greater tubercle. Nevertheless, using contralateral data as a template for repairing an affected proximal humerus might be possible.

Validation of the registration accuracy of navigation-assisted arthroscopic débridement for elbow osteoarthritis

BACKGROUND

The identification and precise removal of bony impingement lesions during arthroscopic débridement arthroplasty for elbow osteoarthritis is technically difficult. Surgical navigation systems, combined with preoperative 3-dimensional (3D) assessment of bony impingements, can provide real-time tracking of the surgical instruments and impingement lesions. This study aims to determine the registration accuracy of the navigation system for the humerus and ulna during elbow arthroscopy.

METHODS

We tested the registration procedure using resin bone models of 3 actual patients with elbow osteoarthritis. We digitized bone surface points using navigation pointers under arthroscopy. We initially performed paired-point registration, digitizing 6 preset anatomical landmarks, and then refined the initial alignment with surface matching registration, digitizing 30 points. The registration accuracy for each trial was evaluated as the mean target registration error in each reference marker. Three observers repeated the registration procedure 5 times each with the 3 specimens (total, 45 trials). The median of the registration accuracy was evaluated in total (45 trials) as the accuracy of the registration procedure. The differences in the registration accuracy among the 3 observers (median of 15 trials) were also examined.

RESULTS

The total registration accuracies were 0.96 mm for the humerus and 0.85 mm for the ulna. No significant differences were found in the registration accuracy for the humerus and ulna among the 3 observers.

CONCLUSIONS

This arthroscopic-assisted registration procedure is sufficiently feasible and accurate for application of the navigation system to arthroscopic débridement arthroplasty in clinical settings.

Restoration of the Patient-Specific Anatomy of the Proximal and Distal Parts of the Humerus: Statistical Shape Modeling Versus Contralateral Registration Method

BACKGROUND

In computer-assisted reconstructive surgeries, the contralateral anatomy is established as the best available reconstruction template. However, existing intra-individual bilateral differences or a pathological, contralateral humerus may limit the applicability of the method. The aim of the study was to evaluate whether a statistical shape model (SSM) has the potential to predict accurately the pretraumatic anatomy of the humerus from the posttraumatic condition.

METHODS

Three-dimensional (3D) triangular surface models were extracted from the computed tomographic data of 100 paired cadaveric humeri without a pathological condition. An SSM was constructed, encoding the characteristic shape variations among the individuals. To predict the patient-specific anatomy of the proximal (or distal) part of the humerus with the SSM, we generated segments of the humerus of predefined length excluding the part to predict. The proximal and distal humeral prediction (p-HP and d-HP) errors, defined as the deviation of the predicted (bone) model from the original (bone) model, were evaluated. For comparison with the state-of-the-art technique, i.e., the contralateral registration method, we used the same segments of the humerus to evaluate whether the SSM or the contralateral anatomy yields a more accurate reconstruction template.

RESULTS

The p-HP error (mean and standard deviation, 3.8° ± 1.9°) using 85% of the distal end of the humerus to predict the proximal humeral anatomy was significantly smaller (p = 0.001) compared with the contralateral registration method. The difference between the d-HP error (mean, 5.5° ± 2.9°), using 85% of the proximal part of the humerus to predict the distal humeral anatomy, and the contralateral registration method was not significant (p = 0.61). The restoration of the humeral length was not significantly different between the SSM and the contralateral registration method.

CONCLUSIONS

SSMs accurately predict the patient-specific anatomy of the proximal and distal aspects of the humerus. The prediction errors of the SSM depend on the size of the healthy part of the humerus.

CLINICAL RELEVANCE

The prediction of the patient-specific anatomy of the humerus is of fundamental importance for computer-assisted reconstructive surgeries.

A Novel Registration-Based Approach for 3D Assessment of Posttraumatic Distal Humeral Deformities

BACKGROUND

With current 3-dimensional (3D) computer-based methods for the assessment of deformities, a surface registration method is applied to superimpose a computer model of the pathological bone onto a mirrored computer model of the contralateral side. However, because of bilateral differences, especially in humeral torsion, such template-based approaches may introduce bias in the assessment of a distal humeral deformity. We hypothesized that a novel registration approach might prove superior to the current approach in reducing such bias, thus yielding improved accuracy of 3D assessment of distal humeral deformities.

METHODS

Three-dimensional triangular surface models were generated from computed tomographic (CT) data of 100 paired humeri without a pathological condition. Humeral segments of varying, predetermined lengths, excluding the distal part of the humerus, were defined. A surface registration algorithm was applied to superimpose the humeral models of both sides based on each selected segment. Humeral contralateral registration (HCR) errors, defined as the residual differences in apparent 3D orientation between the distal parts, were evaluated.

RESULTS

The mean HCR error (and standard deviation) using the distal-most humeral shaft segment to assess the angular orientation was 2.3° ± 1.1 (range, 0.5° to 5.8°). Including the humeral head in the surface registration algorithm, however, as is done currently, resulted in a higher HCR error (p < 0.001). The HCR error using the proximal-most segment was >10° in 20% of the cases and between 5° and 10° in an additional 50% of the cases. By comparison, using the proposed distal-most humeral shaft segment, the HCR error was between 5° and 10° in only 2% of cases, and was never >10°. The proximal segments are nevertheless used in the proposed method for registering humeral length.

CONCLUSIONS

The proposed new approach yields a deformity assessment that is less prone to bias arising from inherent bilateral differences and therefore is more accurate than current surface registration approaches.

CLINICAL RELEVANCE

Accurate 3D assessment is of fundamental importance if computer-based methods are applied in the correction of posttraumatic deformities.

Three-dimensional corrective osteotomies of complex malunited humeral fractures using patient-specific guides

BACKGROUND

Corrective osteotomies of malunited fractures of the proximal and distal humerus are among the most demanding orthopedic procedures. Whereas the restoration of the normal humeral anatomy is the ultimate goal, the quantification of the deformity as well as the transfer of the preoperative plan is challenging. The purpose of this study was to provide a guideline for 3-dimensional (3D) corrective osteotomies of malunited intra-articular fractures of the humerus and a detailed overview of existing and novel instruments to enlarge the toolkit for 3D preoperative planning and intraoperative realization using patient-specific guides.

METHODS

We describe the preoperative 3D deformity analysis, relevant considerations for the preoperative plan, design of the patient-specific guides, and surgical technique of corrective osteotomies of the humerus.

RESULTS

The presented technique demonstrates the benefit of computer-assisted surgery for complex osteotomies of the humerus from a preoperative deformity analysis to the creation of feasible surgical procedures and the generation of patient-specific guides.

CONCLUSIONS

A 3D analysis of a post-traumatic deformity of the humerus, 3D preoperative planning, and use of patient-specific guides facilitate corrective osteotomies of complex malunited humeral fractures.

Does cubitus varus cause morphologic and alignment changes in the elbow joint?

BACKGROUND

In cubitus varus after pediatric supracondylar fracture, late development of trochlear deformity causing additional varus angulation and joint misalignment relating to late complications of the tardy ulnar nerve palsy or posterolateral rotatory instability have been suggested. However, it is unclear whether these morphologic and alignment changes of the elbow joint occur in cubitus varus. The object of this study was to investigate morphologic changes of the bones and alignment changes of the elbow joint in longstanding cubitus varus using 3-dimensional computer bone models created from computed tomography data.

MATERIALS AND METHODS

We studied 14 patients with longstanding cubitus varus after pediatric supracondylar fractures. Three-dimensional bone models of the bilateral humerus, radius, and ulna were created from computed tomography data. We compared the morphology and alignment of the elbow joint between the affected side and contralateral unaffected side.

RESULTS

The posterior trochlea, distal part of the lateral capitellum, diameters of the radial head, and articular surface of the ulna in cubitus varus were larger than those of the contralateral elbow. In the ulna, the convex portion of the trochlear notch shifted laterally in cubitus varus. Joint alignment in cubitus varus was affected by a shift of the ulna to a more distal and medial position with external rotation and flexion.

CONCLUSIONS

In longstanding cubitus varus, the morphology and alignment of the elbow joint are observed to differ from those of the normal side.

Kinematics and laxity of a linked total elbow arthroplasty following computer navigated implant positioning

Aseptic loosening in total elbow arthroplasty (TEA) remains the most common cause of long-term failure. While several different mechanisms of implant loosening have been suggested, it is likely that one important underlying cause is implant malpositioning, resulting in changes in joint kinematics and loading. Although use of computer navigation has been shown to improve component positioning in other joints, no such system currently exists for the elbow. This study used real-time computer feedback for humeral, ulnar, and radial component positioning in 11 cadaveric extremities. An elbow motion simulator evaluated joint kinematics. Endosteal abutment of the stems of the humeral and ulnar components precluded optimal positioning in 5 and 6 specimens, respectively. Loss of the normal valgus angulation following elbow arthroplasty (p < 0.05) suggests that errors in humeral component positioning translate directly into changes in joint kinematics during active motion. These findings suggest that although computer navigation can reproduce normal joint kinematics, optimal implant positioning may require a TEA system which allows for some modularity to accommodate the normal variations in osseous morphology of the elbow.

A HUMERAL COORDINATE SYSTEM FOR IN VIVO 3-D KINEMATICS OF THE GLENOHUMERAL JOINT

The aim of this study was to define axes from clearly identifiable landmarks on the proximal aspect of the humerus and to compare these for reasonable best alternatives to the use of the humeral canal and elbow epicondylar axes to define a humeral coordinate frame (HCF). The elbow epicondylar axis (EC) and six different humeral canal axes (HC) based on varying lengths of humerus were quantified from 21 computed tomography (CT) scans of humeri. Six additional axes were defined using the proximal humerus only. These included a line from the center of a sphere fit on the humeral head to the 3D surface area centroid of the greater tubercle region, (GT). The inclinations of these axes relative to EC were calculated. GT was found to be the most closely aligned to EC (13.4° ± 6.8°). The inclinations of the other axes ranged from 36.3° to 86.8°. The HC axis orientation was found to be insensitive to humeral shaft lengths (variability, within average: 0.6°). This was chosen as one of two axes for the HCF. It was also the most inter-subject related axis to EC with inclination standard deviation of ±1.8°. EC was therefore predicted from this such that if the superior axis [1 0 0] of an image scan is maintained and the humerus rotated to make its quantified HC align superiorly in the direction [0.98 0.01 0.01], then its EC axis lies laterally in the direction [0 0 1]. This study demonstrates that it is possible with confidence to apply an orthogonal coordinate frame to the humerus based on proximal imaging data only.

Stem abutment affects alignment of the humeral component in computer-assisted elbow arthroplasty

OBJECTIVES AND HYPOTHESIS

The humeral component in total elbow arthroplasty has limited geometric modularity, and the extent to which this affects accurate positioning is unknown. The objectives of this study were to (1) validate the accuracy of a computer-assisted implant alignment technique, and (2) identify variations in distal humeral morphology that affected computer-assisted implant alignment. This was achieved by implanting both an unmodified humeral component and an implant with a reduced stem using computer assistance. We hypothesized that implantation of a humeral component with a reduced stem length would be more accurate than implantation of the standard length stem. In addition, we hypothesized that the variation in flexion-extension (FE) varus-valgus angulation would significantly affect computer-assisted implant alignment.

MATERIALS AND METHODS

Computer-assisted alignment of the implant articulating axis with the humeral FE axis was performed on 13 cadaveric humeri for both the regular and modified humeral component. Navigation was based on alignment of the prosthesis with a preoperative plan and registration of this plan to the humerus.

RESULTS

Implant alignment was significantly improved for the reduced stem. Alignment error of the reduced stem averaged 1.3 ± 0.5 mm in translation and 1.2° ± 0.4° in rotation, compared with 1.9 ± 1.1 mm and 3.6° ± 2.1° for the regular stem. Humeral varus-valgus angulation significantly affected alignment of the unmodified stem.

DISCUSSION

A humeral component with a fixed valgus angulation cannot be accurately positioned in a consistent fashion without sacrificing alignment of the FE axis. Improved accuracy of implant placement can be achieved by introducing a family of humeral components, with 3 valgus angulations of 0°, 4° and 8°.

Image-based navigation improves the positioning of the humeral component in total elbow arthroplasty

HYPOTHESIS

Implant alignment in total elbow arthroplasty (TEA) is a challenging and error-prone process using conventional techniques. Identification of the flexion-extension (FE) axis is further complicated for situations of bone loss. This study evaluated the accuracy of humeral component alignment in TEA. We hypothesized that an image-based navigation system would improve humeral component positioning, with navigational errors less than or approaching 2.0 mm and 2.0 degrees .

MATERIALS AND METHODS

Implantation of a modified commercial TEA humeral component was performed with and without navigation on 11 cadaveric distal humeri. Navigated alignment was based on positioning the humeral component with the aid of a computed tomography (CT)-based preoperative plan registered to landmarks on the distal humerus. Alignment was performed under 2 scenarios of bone quality: (1) an intact distal humerus, and (2) a distal humerus without articular landmarks.

RESULTS

Navigation significantly improved implant alignment accuracy (P < .001). Navigated implant alignment was 1.2 +/- 0.3 mm in translation and 1.3 degrees +/- 0.3 degrees in rotation for the intact scenario. For the bone loss scenario, navigated alignment error was 1.1 +/- 0.5 mm and 2.0 degrees +/- 1.3 degrees . Non-navigated alignment was 3.1 +/- 1.3 mm and 5.0 degrees +/- 3.8 degrees for the intact scenario and 3.0 +/- 1.6 mm and 12.2 degrees +/- 3.3 degrees for the bone loss scenario.

DISCUSSION

Image-based navigation improves the accuracy and reproducibility of humeral component placement in TEA. Implant alignment errors for the navigated alignments were below the target of 2.0 degrees and 2 mm that is considered standard for most navigation systems. Non-navigated implant alignment error was significantly greater for the bone loss scenario compared with the intact scenario.

CONCLUSIONS

Implant malalignment may increase the likelihood of early implant wear, instability, and loosening. Improved implant positioning will likely lead to fewer complications and greater prosthesis longevity.

Computer assisted surgery of the distal humerus can employ contralateral images for pre-operative planning, registration, and surgical intervention

BACKGROUND

Bone loss at the distal humerus can lead to errors in the identification of the elbow's flexion-extension axis. Referencing the anatomy of the contralateral (uninjured) elbow may prove beneficial in accurately defining this axis. The objective of this study was to compare distal humeral morphology between paired specimens and determine whether geometric differences exist.

METHODS

Medical CT images of 25 paired, dry cadaveric, distal humeri were acquired and a range of anatomic characteristics were measured, following registration of each pair to a common coordinate system.

RESULTS

The anthropometric features of the distal humerus were similar from side-to-side, with differences on the order of 1.0 degrees and 0.5 mm.

CONCLUSIONS

Preoperative imaging of the contralateral normal elbow may be employed in patients with peri-articular bone loss, where referencing anatomic landmarks of the injured side is not possible.