Biomechanical evaluation of two-part surgical neck fractures of the humerus fixed by an angular stable locked intramedullary nail

A comparative study of locking plate combined with minimally invasive plate osteosynthesis and intramedullary nail fixation in the treatment of Neer classification of two-part and three-part fractures of the proximal humerus

OBJECTIVE

To compare the clinical efficacy of the minimally invasive locking plate technique (Philos plate) and interlocking intramedullary nailing technique (TRIGEN intramedullary nail) in the treatment of Neer two-part and three-part proximal humeral fractures.

METHODS AND MATERIALS

The clinical data of 60 patients with Neer two-part and three-part proximal humerus fractures admitted to the hospital from April 2017 to April 2021 were retrospectively analyzed. Thirty-two patients were treated with the minimally invasive locking plate technique (minimally invasive plate group), and 28 patients were treated with the interlocking intramedullary nailing technique (intramedullary nail group). The operation time, intraoperative blood loss, incision length, fracture healing time, and postoperative complications were compared between the two groups. The ASES score and Constant-Murley score were used to evaluate the shoulder joint function of the two groups one year after surgery.

RESULTS

All 60 patients were followed up for 12 to 24 months, with an average of 16 months. There was no significant difference in operation time, intraoperative blood loss, incision length, or fracture healing time between the two groups (P > 0.05). The incidence of postoperative complications in the intramedullary nail group was significantly lower than that in the minimally invasive steel plate group, and the difference between the groups was statistically significant (P < 0.05). There was no significant difference in the ASES score or Constant-Murley score between the two groups one year after surgery (P > 0.05).

CONCLUSION

The use of the minimally invasive locking plate technique and interlocking intramedullary nailing technique in the treatment of Neer two-part and three-part proximal humerus fractures has the advantages of a small incision, less blood loss, and a high fracture healing rate, and both can achieve satisfactory clinical effects. The internal nail technique is more convenient than the minimally invasive locking plate technique in controlling postoperative complications.

Helical Plating Compared with Straight Plating and Nailing for Treatment of Proximal Third Humeral Shaft Fractures-A Biomechanical Study

Background and Objectives: The surgical treatment of proximal humeral shaft fractures usually considers application of either long straight plates or intramedullary nails. By being able to spare the rotator cuff and avoid the radial nerve distally, the implementation of helical plates might overcome the downsides of common fixation methods. The aims of the current study were (1) to explore the biomechanical competence of different plate designs and (2) to compare their performance versus the alternative treatment option of using intramedullary nails. Materials and Methods: Twenty-four artificial humeri were assigned to the following four groups for simulation of an unstable proximal humeral shaft fracture and instrumentation: Group 1 (Straight-PHILOS), Group 2 (MULTILOC-Nail), Group 3 (45°-Helical-PHILOS), and Group 4 (90°-Helical-PHILOS). All specimens underwent non-destructive, quasi-static biomechanical testing under loading in axial compression, torsion in internal/external rotation, and pure bending in four directions, accompanied by motion tracking. Results: Axial stiffness/displacement in Group 2 was significantly higher/smaller than in all other groups (p ≤ 0.010). Torsional displacement in Group 2 was significantly bigger than in all other groups (p ≤ 0.017). Significantly smaller coronal plane displacement was identified in Group 2 versus all other groups (p < 0.001) and in Group 4 versus Group 1 (p = 0.022). Significantly bigger sagittal plane displacement was detected in Group 4 versus all other groups (p ≤ 0.024) and in Group 1 versus Group 2 (p < 0.001). Conclusions: Intramedullary nails demonstrated higher axial stiffness and smaller axial interfragmentary movements compared with all investigated plate designs. However, they were associated with bigger torsional movements at the fracture site. Although 90°-helical plates revealed bigger interfragmentary movements in the sagittal plane, they demonstrated improved resistance against displacements in the coronal plane when compared with straight lateral plates. In addition, 45°-helical plates manifested similar biomechanical competence to straight plates and may be considered a valid alternative to the latter from a biomechanical standpoint.

Treatment of Metaphyseal Defects in Plated Proximal Humerus Fractures with a New Augmentation Technique-A Biomechanical Cadaveric Study

Background and Objectives: Unstable proximal humerus fractures (PHFs) with metaphyseal defects-weakening the osteosynthesis construct-are challenging to treat. A new augmentation technique of plated complex PHFs with metaphyseal defects was recently introduced in the clinical practice. This biomechanical study aimed to analyze the stability of plated unstable PHFs augmented via implementation of this technique versus no augmentation. Materials and Methods: Three-part AO/OTA 11-B1.1 unstable PHFs with metaphyseal defects were created in sixteen paired human cadaveric humeri (average donor age 76 years, range 66-92 years), pairwise assigned to two groups for locked plate fixation with identical implant configuration. In one of the groups, six-milliliter polymethylmethacrylate bone cement with medium viscosity (seven minutes after mixing) was placed manually through the lateral window in the defect of the humerus head after its anatomical reduction to the shaft and prior to the anatomical reduction of the greater tuberosity fragment. All specimens were tested biomechanically in a 25° adduction, applying progressively increasing cyclic loading at 2 Hz until failure. Interfragmentary movements were monitored by motion tracking and X-ray imaging. Results: Initial stiffness was not significantly different between the groups, p = 0.467. Varus deformation of the humerus head fragment, fracture displacement at the medial humerus head aspect, and proximal screw migration and cut-out were significantly smaller in the augmented group after 2000, 4000, 6000, 8000 and 10,000 cycles, p ≤ 0.019. Cycles to 5° varus deformation of the humerus head fragment-set as a clinically relevant failure criterion-and failure load were significantly higher in the augmented group, p = 0.018. Conclusions: From a biomechanical standpoint, augmentation with polymethylmethacrylate bone cement placed in the metaphyseal humerus head defect of plated unstable PHFs considerably enhances fixation stability and can reduce the risk of postoperative complications.

Biomechanical analysis of helical versus straight plating of proximal third humeral shaft fractures

BACKGROUND

Proximal humeral shaft fractures are surgically challenging and plate osteosynthesis with a long straight plate is one operative treatment option in these patients although endangering the radial nerve distally. Helical plates potentially avoid the radial nerve by twisting around the humeral shaft. Aim of the study was to investigate in a human cadaveric model the biomechanical competence of helical plates versus straight lateral plates used for fixation of proximal third comminuted humeral shaft fractures.

METHODS

Eight pairs of humeral cadaveric humeri were instrumented using either a long 90°-helical plate (Group1) or a straight long PHILOS plate (Group2). An unstable proximal humeral shaft fracture was simulated by means of a 5 cm osteotomy gap. All specimens were tested under quasi-static loading in axial compression, internal and external rotation, and bending in four directions. Subsequently, progressively increasing cyclic loading in internal rotation until failure was applied and interfragmentary movements were monitored by motion tracking.

RESULTS

During static testing flexion/extension deformation in Group1 was significantly higher, however, varus/valgus deformation as well as shear and torsional displacement under torsional load remained statistically indifferent between both groups. During cyclic testing shear and torsional displacements were both significantly higher in Group1 compared to Group 2. However, cycles to catastrophic failure remained statistically indifferent between the groups.

CONCLUSIONS

From a biomechanical perspective, although 90°-helical plating is associated with higher initial stability against varus/valgus collapse and comparable endurance under dynamic loading, it demonstrates lower resistance to flexion/extension and internal rotation with bigger shear interfragmentary displacements versus straight lateral plating and, therefore, cannot be considered as its real alternative. Alternative helical plate designs should be investigated in the future.

Is Bridge Plating of Comminuted Humeral Shaft Fractures Advantageous When Using Compression Plates with Three versus Two Screws per Fragment? A Biomechanical Cadaveric Study

Background

Minimally invasive plate osteosynthesis (MIPO) is one of the generally accepted surgical techniques for the treatment of humeral shaft fractures. However, despite the high bone union rate, a variety of complications are still prevailing. Moreover, the current literature lacks data comparing the anterolateral MIPO approach using dynamic compression plates accommodating different numbers of screws. The aim of this study was to analyze the biomechanical performance of comminuted humeral shaft fractures fixed with dynamic compression plates using either two or three screws per fragment.

Methods

Six pairs of fresh-frozen human cadaveric humeri from donors aged 66.8 ± 5.2 years were randomized to two paired study groups for simulation of bridge-plated comminuted shaft fracture type AO/OTA 12-C1/2/3 without interfragmentary bony support, using a dynamic compression plate positioned on the anterolateral surface and fixed with two (group 1) or three (group 2) screws per fragment. All specimens underwent nondestructive quasistatic biomechanical testing under lateral bending, anterior bending, axial bending, and torsion in internal rotation, followed by progressively increasing cyclic torsional loading in internal rotation until failure.

Results

Initial stiffness of the plated specimens in lateral bending, anterior bending, axial bending, and torsion was not significantly different between the groups (P ≥ 0.22). However, cycles to 10°, 15°, and 20° torsional deformation and cycles to construct failure were significantly higher in group 2 compared with group 1 (P ≤ 0.03).

Conclusions

From a biomechanical perspective, no significant superiority is identified in terms of primary stability when using two or three screws per fragment for bridge compression plating of comminuted humeral shaft fractures. However, three-screw configurations provide better secondary stability and maintain it with a higher resistance towards loss of reduction under dynamic loading. Therefore, the use of a third screw may be justified when such better secondary stability is required.

Dynamic locking screws in proximal humeral plate osteosynthesis demonstrate superior fixation properties: a biomechanical study

Purpose

Angular stable implants reduced the complication rate in the treatment of humeral head fractures. But the failure rate is still high. To further reduce the risk of cut-out, cement augmentation of screws was introduced. A reason for failure of plate osteosynthesis might be the extremely high stiffness of the screw-plate interface leading to a loss of reduction and cut-out of screws. A more homogeneous distribution of the forces on all screws may avoid secondary dislocation. We hypothesize that dynamic osteosynthesis minimizes screw loosening and results in a higher load to failure than standard locking screws.

Methods

Twelve paired human humerus specimens were analysed. A standardized three-part fracture model with a metaphyseal defect was simulated. Within each pair of humeri, one was fixed with a Philos plate and standard locking screws (LS), whereas the other humerus was fixed with a Philos plate and dynamic locking screws (DLS). A cyclic varus-bending test or a rotation test with increasing loading force was performed until failure of the screw-bone-fixation.

Results

In the varus bending test, pairs failed by screw loosening in the humeral head. The LS-group reached 2901 (601–5201) load cycles until failure, while the DLS-group failed after 3731 (2001–5601) cycles. This corresponds to a median loading of 195 N for the LS-group and 235 N for the DLS-group (p = 0.028). In the rotation test the LS-group reached a median of 1101 (501–1501) load cycles until failure of fixation occurred, while the DLS-group failed after 1401 (401–2201) cycles (p = 0.225).

Conclusions

Plate fixation using dynamic locking screws for the treatment of proximal humerus fractures demonstrated more load cycles until failure compared to standard locking plate osteosynthesis.

How to improve the outcomes of surgically treated proximal humeral osteoporotic fractures? A narrative review

Proximal humeral fractures (PHF) are the third most common non-vertebral fragility fractures after hip and distal radius. It still controversial which treatment might be more appropriate, and surgically treated outcomes depends also on an appropriate technique. In order to clarify surgical indications, tips and pitfall a narrative review was conducted. Pinning, external fixation, plating and internal fixators has each one its advantages and disadvantages. During the procedure an appropriate use of the fixation device and handling of the soft tissue might be associated with better outcomes. Calcar comminution, varus angulation, medial dislocation of the shaft, fracture-dislocation are factors that could lead to choose a replacement. Hemiarthroplasty and reverse total shoulder arthroplasty are the most common prosthesis used in PHF. The restoration of humeral length and tuberosities might lead to an improvement in clinical outcomes and prosthesis survivorship.

Operative treatment of 2-part surgical neck fractures of the proximal humerus (AO 11-A3) in the elderly: Cement augmented locking plate Philos™ vs. proximal humerus nail MultiLoc®

Background

Proximal humeral fractures are with an incidence of 4–5 % the third most common fractures in the elderly. In 20 % of humeral fractures there is an indication for surgical treatment according to the modified Neer-Criteria. A secondary varus dislocation of the head fragment and cutting-out are the most common complications of angle stable locking plates in AO11-A3 fractures of the elderly. One possibility to increase the stability of the screw-bone-interface is the cement augmentation of the screw tips. A second is the use of a multiplanar angle stablentramedullary nail that might provide better biomechanical properties after fixation of 2-part-fractures. A comparison of these two treatment options augmented locking plate versus multiplanar angle stable locking nail in 2-part surgical neck fractures of the proximal humerus has not been carried out up to now.

Methods/Design

Forty patients (female/male, ≥60 years or female postmenopausal) with a 2-part-fracture of the proximal humerus (AO type 11-A3) will be randomized to either to augmented plate fixation group (PhilosAugment) or to multiplanar intramedullary nail group (MultiLoc). Outcome parameters are Disabilities of the Shoulder, Arm and Hand-Score (DASH) Constant Score (CS), American Shoulder and Elbow Score (ASES), Oxford Shoulder Score (OSS), Range of motion (ROM) and Short Form 36 (SF-36) after 3 weeks, 6 weeks, 3 months, 6 months, 12 and 24 months.

Discussion

Because of the lack of clinical studies that compare cement augmented locking plates with multiplanar humeral nail systems after 2-part surgical neck fractures of the proximal humerus, the decision of surgical method currently depends only on surgeons preference. Because only a randomized clinical trial (RCT) can sufficiently answer the question if one treatment option provides advantages compared to the other method we are planning to perform a RCT.

Trial registration

Clinical Trial (NCT02609906), November 18, 2015, registered retrospectively.

Is there any advantage in placing an additional calcar screw in locked nailing of proximal humeral fractures?

BACKGROUND

The objective of this study was to evaluate the biomechanical effect of an additional unlocked calcar screw compared to a standard setting with three proximal humeral head screws alone for fixation of an unstable 2-part fracture of the surgical neck.

HYPOTHESIS

The additional calcar screw improves stiffness and failure load.

METHODS

Fourteen fresh frozen humeri were randomized into two equal sized groups. An unstable 2-part fracture of the surgical neck was simulated and all specimens were fixed with the MultiLoc(®)-nail. Group I represented a basic screw setup, with three locked head screws and two unlocked shaft screws. Group II was identical with a supplemental unlocked calcar screw (CS). Stiffness tests were performed in torsional loading, as well as in axial and in 20° abduction/20° adduction modes. Subsequently cyclic loading and load-to-failure tests were performed. Resulting stiffness, displacement under cyclic load and ultimate load were compared between groups using the t-test for independent variables (α=0.05).

RESULTS

No significant differences were observed between the groups in any of the biomechanical parameters. Backing out of the CS was observed in three cases.

DISCUSSION

The use of an additional unlocked calcar screw does not provide mechanical benefit in locked nailing of an unstable 2-part fracture of the surgical neck.

Comparison of modified Hackethal bundle nailing versus anterograde nailing for fixation of surgical neck fractures of the humerus: retrospective study of 105 cases

INTRODUCTION

Intramedullary fixation of displaced surgical neck fractures of the humerus can be performed either by retrograde pinning or anterograde nailing. The goal of the current study was to compare the postoperative reduction and stability obtained with these two techniques.

HYPOTHESIS

Intramedullary nailing will provide the best reduction and stabilization of these fractures.

PATIENTS AND METHODS

This was a multicenter retrospective study that included patients with sub-tuberosity fractures with or without greater tuberosity fragment. These patients were treated either by retrograde Hackethal type pinning (group 1) or Telegraph anterograde nailing (group 2). To be included, patients needed to have A/P and lateral X-rays that had been taken before the surgery, immediately post-operative, between four and six weeks post-operative, and at the last follow-up. The outcomes were head angulation, translation and greater tuberosity position.

RESULTS

One hundred and five patients (40 retrograde pinning and 65 anterograde nailing) with an average age of 69 years (18-97 years) were included. The pre-operative fracture displacement was similar between the two groups. After the surgery, the A/P head angulation had been corrected in 72.5% of patients in group 1 and 84% in group 2 (no significant difference). Translation was still present in 17.5% of patients in group 1 and 1.5% in group 2 (P<0.05). At the last follow-up, union was achieved without residual angulation on lateral X-rays in 71% of patients in group 1 and 88% in group 2 (P<0.05). The fractures had healed with residual translation is 19.5% of patients in group 1 and 3% in group 2 (P<0.05).

DISCUSSION AND CONCLUSION

In cases of displaced surgical neck fractures with or without a greater tuberosity fragment, anterograde nailing provides better reduction and stability than retrograde pinning. However, fixation of the greater tuberosity fragment must be improved.

LEVEL OF EVIDENCE

IV (retrospective comparative study).

A comprehensive update on current fixation options for two-part proximal humerus fractures: a biomechanical investigation

BACKGROUND

Recent advancements in implant technology offer updated options for surgical management that have been rapidly adopted into clinical practice. The objective of this study is to biomechanically test and compare the current fixation options available for surgical fixation of two-part proximal humerus fractures and establish load to failure and stiffness values.

METHODS

Sixteen match-paired (32 total) fresh-frozen, cadaveric specimens were randomized to receive 1 of 4 fixation constructs following creation of an AO/OTA Type 11A3 (two-part) proximal humerus fractures. Fixation constructs tested consisted of 3.5 mm fixed angle plate (3.5-FAP), 4.5 mm fixed angle plate (4.5-FAP), humeral intramedullary nail (IMN), and a humeral intramedullary nail with a fixed angle blade (IMN-FAB). Specimen bone density was measured to ensure no adequate, non-osteoporotic bone. Constructs were tested for stiffness and ultimate load to failure and compared via one-way ANOVA analysis with subsequent post hoc Tukey HSD multiple group comparison statistical analysis.

RESULTS

The IMN-FAB construct was significantly stiffer than the 3.5-FAP construct (123.8 vs. 23.9, p<0.0001), the 4.5-FAP construct (123.8 vs. 33.3, p<0.0001) and the IMN construct (123.8 vs. 60.1, p=0.005). The IMN-FAB construct reported a significantly higher load to failure than the 3.5-FAB construct (4667.3 N vs. 1756.9 N, p<0.0001), and the 4.5-FAP construct (4667.3 N vs. 2829.4 N, p=0.019, Table 2). The IMN construct had a significantly higher load to failure than the 3.5-FAP construct (3946.8 vs. 1756.9, p=0.001, Table 2).

CONCLUSION

Biomechanical testing of modern fixation options for two-part proximal humerus fracture exhibited that the stiffest and highest load to failure construct was the IMN-FAB followed by the IMN, 3.5-FAP and then the 4.5-FAP constructs. However, prospective clinical trials with longer-term follow-up are required for definitive assessment of the ideal fixation construct for surgical management of two-part proximal humerus fractures.

Proximal humeral fracture treatment in adults

Most proximal humeral fractures affect elderly patients and can be treated nonoperatively with good functional outcomes.The treatment of displaced three and four-part fractures remains controversial and depends on a variety of underlying factors related to the patient (e.g., comorbidity, functional demand), the fracture (e.g., osteoporosis), and the surgeon (e.g., experience).Throughout the literature, open reduction and locking plate osteosynthesis is associated with considerable complication rates, particularly in the presence of osteoporosis.Low local bone mineral density, humeral head ischemia, residual varus displacement, insufficient restoration of the medial column, and nonanatomic reduction promote failure of fixation and impair functional outcome.The outcome of hemiarthroplasty is closely related to tuberosity healing in an anatomic position to enable the restoration of rotator cuff function. Reverse shoulder arthroplasty may provide satisfactory shoulder function in geriatric patients with preexisting rotator cuff dysfunction or after the failure of first-line treatment.

Nailing of three- and four-part fractures of the humeral head -- long-term results

BACKGROUND AND PURPOSE

Long term outcome of the treatment of displaced complex fractures of humeral head is rare in the literature especially in greater cohorts. Main purpose of our study was the assessment of long term results of intramedullary nailing of 3-4 part fractures.

PATIENTS AND METHODS

137 patients with 137 three or four-part fractures of the humeral head treated by intramedullary nailing were reassessed after an average follow-up time of 57 (27-93) months. The whole cohort consisted of 85 three-part fractures, 38 four-part fractures and 14 fracture-dislocations. Radiographic and clinical outcome - absolute Constant score (CS(abs)) and relative Constant score (compared to the contralateral side - CS(rel)) were evaluated. The rate of complications was recorded. Analysis of the influence of quality of achieved reduction on final functional result and on the development of complications was performed.

RESULTS

125 fractures healed uneventfully. Mean long term CS(rel) was 81% of the unaffected side. Mean CS(rel) was 85% in 3-part fractures, 73% in four-part fractures, 80% in three-part fracture-dislocations and 70% in four-part fracture-dislocations. 96 (70%) patients achieved excellent or good results (CS(rel) higher than 80%), 17 (12.4%) satisfactory results and 24 (17.5%) poor results (CS(rel) less than 60%). No significant difference was observed in functional results between different age groups. No incidence of non-union was observed, 4 losses of reduction were encountered. We observed 17 cases of complete humeral head necrosis, 14 of them in the group of 4-part fractures. Reduction quality strongly influenced functional result and development of head necrosis. In the group of excellent reduction mean CS(rel) was 88% and the rate of necrosis was 2%. Moderate reduction quality deteriorated CS(rel) to 70% and head necrosis rate rose up to 28%. If reduction was poor, mean CS(rel) was 52% and the rate of complete necrosis rose to 60%.

CONCLUSION

Long term results confirmed nailing as appropriate treatment strategy for all types of humeral head fractures with limitation of excellent reduction in every age group. Moderate or even poor reduction significantly deteriorates functional results and increases rate of complete necrosis of the humeral head. If good reduction cannot be achieved, treatment strategy should be changed.

Short- or long-stem prosthesis for intramedullary bypass of proximal humeral fractures with severe metaphyseal bone loss: evaluation of primary stability in a biomechanical model

BACKGROUND

Proximal humeral fractures with substantial metaphyseal comminution are challenging to treat. In the elderly with osteoporotic bone, arthroplasty sometimes remains the only valuable option; however, the minimally required length of stem fixation is not known. The aim of this study was to investigate the primary stability of cemented short- and long-stem prostheses with different intramedullary fracture bypass lengths.

MATERIALS AND METHODS

Osteoporotic composite bone models of the humerus (Synbone, Malans, Switzerland) with 3 different fracture levels (group A, 6 cm distal to surgical neck; group B, 7 cm distal to surgical neck; and group C, 8 cm distal to surgical neck) were prepared with a cemented standard short (S)- or long (L)-stem prosthesis and were tested for torque to failure. As a reference, we used models with intact bone (group R-O) and a short-stem prosthesis implanted at the surgical neck (group R-P). The radiographic bypass index (BI) was calculated before testing (fracture level to stem tip [in millimeters]/outer cortical diameter at fracture level [in millimeters]).

RESULTS

The resulting BIs of each group were as follows: 1.7 in group A-S, 3.4 in group A-L, 1.4 in group B-S, 3.2 in group B-L, 1.0 in group C-S, and 2.9 in group C-L. Compared with group R-O, the torques to failure of groups B-S and C-S were significantly lower, whereas only group C-S was significantly weaker than group R-P (P < .01). Comparing short- and long-stem bypasses of different fracture heights, we found that only group C-L showed a significantly higher resistance to torque (P < .01).

CONCLUSIONS

A short-stem bypass with a BI of 1.7 was sufficient for primary stability tested by torque to failure in this biomechanical setting. For smaller BIs, a long-stem prosthesis should be considered.

LEVEL OF EVIDENCE

Basic science study, biomechanics.

Internal fixation of fractures of the proximal humerus with the MultiLoc nail

OBJECTIVE

Anatomical reduction of two- to four-part fractures of the proximal humerus using indirect reduction techniques. Intramedullary fixation with a short humerus nail. Restoration of a stable bone-implant construct that enables early functional after-treatment.

INDICATIONS

Displaced and unstable two- to four-part fractures of the proximal humerus. Fractures of the proximal humerus extending in the humeral diaphysis (use a long nail). Ipsilateral combined lesions of the proximal humerus and the humeral diaphysis (use a long nail).

CONTRAINDICATIONS

Poor physical and/or mental status. Critical soft tissue conditions in the area near the surgical site. Local soft tissue infection. Pre-existing severe osteoarthritis of the shoulder joint; severe shoulder stiffness. Head-split fractures of the humerus head that cannot be reduced.

SURGICAL TECHNIQUE

Exposure of the fracture using an anterior acromial approach and determination of the correct nail entrance point. Anatomic fracture reduction using indirect reduction techniques. Stable fixation using an intramedullary MultiLoc® nail. Determination of the proximal locking configuration depending on the fracture morphology. Distal locking with angle-stable option. POST-OPERATIVE TREATMENT: Post-operative radiographs for documentation of the surgical result and implant position. Use of an arm sling for 7-10 days. Active and passive exercises of the shoulder joint starting on day 1. Shoulder abduction limited to 60° for 2 weeks. Subsequent abduction to 90° until the 4th week. Subsequent active mobilisation without restrictions. Weight bearing and sporting activities after 3 months. Radiological evaluation after 2, 6 and 12 weeks.

RESULTS

During a 6-month period, 160 patients were documented in a prospective clinical multicentre study. According to the AO classification, there were 36% A-type fractures, 41% B- and 23% C-type injuries. A 6-month follow-up was available for 17 patients. The mean age of these patients was 67 years. One patient had an A-type fracture. There were ten B- and six C-type fractures. At the time of follow-up, the mean Constant score was 66 points. Radiographically, all fractures had healed. Intra-articular screw penetration and loss of reduction were both observed once.

The effect of in situ augmentation on implant anchorage in proximal humeral head fractures

INTRODUCTION

Fracture fixation in patients suffering from osteoporosis is difficult as sufficient implant anchorage is not always possible. One method to enhance implant anchorage is implant/screw augmentation with PMMA-cement. The present study investigated the feasibility of implant augmentation with PMMA-cement to enhance implant anchorage in the proximal humerus.

MATERIALS AND METHODS

A simulated three part humeral head fracture was stabilised with an angular stable plating system in 12 pairs of humeri using six head screws. In the augmentation group the proximal four screws were treated with four cannulated screws, each augmented with 0.5ml of PMMA-cement, whereas the contra lateral side served as a non-augmented control. Specimens were loaded in varus-bending or axial-rotation using a cyclic loading protocol with increasing load magnitude until failure of the osteosynthesis occurred.

RESULTS

Augmented specimens showed a significant higher number of load cycles until failure than non-augment specimens (varus-bending: 8516 (SD 951.6) vs. 5583 (SD 2273.6), P=0.014; axial-rotation: 3316 (SD 348.8) vs. 2050 (SD 656.5), P=0.003). Non-augmented specimens showed a positive correlation of load cycles until failure and measured bone mineral density (varus-bending: r=0.893, P=0.016; axial-rotation: r=0.753, P=0.084), whereas no correlation was present in augmented specimens (varus-bending: r=0,258, P=0.621; axial-rotation r=0.127, P=0.810).

CONCLUSION

These findings suggest that augmentation of cannulated screws is a feasible method to enhance implant/screw anchorage in the humeral head. The improvement of screw purchase is increasing with decreasing bone mineral density.