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Bone & Joint Research
Vol. 12, Issue 2 | Pages 103 - 112
1 Feb 2023
Walter N Szymski D Kurtz SM Lowenberg DW Alt V Lau E Rupp M

Aims

The optimal choice of management for proximal humerus fractures (PHFs) has been increasingly discussed in the literature, and this work aimed to answer the following questions: 1) what are the incidence rates of PHF in the geriatric population in the USA; 2) what is the mortality rate after PHF in the elderly population, specifically for distinct treatment procedures; and 3) what factors influence the mortality rate?

Methods

PHFs occurring between 1 January 2009 and 31 December 2019 were identified from the Medicare physician service records. Incidence rates were determined, mortality rates were calculated, and semiparametric Cox regression was applied, incorporating 23 demographic, clinical, and socioeconomic covariates, to compare the mortality risk between treatments.


Bone & Joint Research
Vol. 7, Issue 6 | Pages 422 - 429
1 Jun 2018
Acklin YP Zderic I Inzana JA Grechenig S Schwyn R Richards RG Gueorguiev B

Aims

Plating displaced proximal humeral fractures is associated with a high rate of screw perforation. Dynamization of the proximal screws might prevent these complications. The aim of this study was to develop and evaluate a new gliding screw concept for plating proximal humeral fractures biomechanically.

Methods

Eight pairs of three-part humeral fractures were randomly assigned for pairwise instrumentation using either a prototype gliding plate or a standard PHILOS plate, and four pairs were fixed using the gliding plate with bone cement augmentation of its proximal screws. The specimens were cyclically tested under progressively increasing loading until perforation of a screw. Telescoping of a screw, varus tilting and screw migration were recorded using optical motion tracking.


Bone & Joint Research
Vol. 5, Issue 10 | Pages 470 - 480
1 Oct 2016
Sabharwal S Patel NK Griffiths D Athanasiou T Gupte CM Reilly P

Objectives. The objective of this study was to perform a meta-analysis of all randomised controlled trials (RCTs) comparing surgical and non-surgical management of fractures of the proximal humerus, and to determine whether further analyses based on complexity of fracture, or the type of surgical intervention, produced disparate findings on patient outcomes. Methods. A systematic review of the literature was performed identifying all RCTs that compared surgical and non-surgical management of fractures of the proximal humerus. Meta-analysis of clinical outcomes was performed where possible. Subgroup analysis based on the type of fracture, and a sensitivity analysis based on the type of surgical intervention, were also performed. Results. Seven studies including 528 patients were included. The overall meta-analysis found that there was no difference in clinical outcomes. However, subgroup and sensitivity analyses found improved patient outcomes for more complex fractures managed surgically. Four-part fractures that underwent surgery had improved long-term health utility scores (mean difference, MD 95% CI 0.04 to 0.28; p = 0.007). They were also less likely to result in osteoarthritis, osteonecrosis and non/malunion (OR 7.38, 95% CI 1.97 to 27.60; p = 0.003). Another significant subgroup finding was that secondary surgery was more common for patients that underwent internal fixation compared with conservative management within the studies with predominantly three-part fractures (OR 0.15, 95% CI 0.04 to 0.63; p = 0.009). Conclusion. This meta-analysis has demonstrated that differences in the type of fracture and surgical treatment result in outcomes that are distinct from those generated from analysis of all types of fracture and surgical treatments grouped together. This has important implications for clinical decision making and should highlight the need for future trials to adopt more specific inclusion criteria. Cite this article: S. Sabharwal, N. K. Patel, D. Griffiths, T. Athanasiou, C. M. Gupte, P. Reilly. Trials based on specific fracture configuration and surgical procedures likely to be more relevant for decision making in the management of fractures of the proximal humerus: Findings of a meta-analysisBone Joint Res 2016;5:470–480. DOI: 10.1302/2046-3758.510.2000638


The Bone & Joint Journal
Vol. 96-B, Issue 5 | Pages 574 - 579
1 May 2014
Talbot CL Ring J Holt EM

We present a review of claims made to the NHS Litigation Authority (NHSLA) by patients with conditions affecting the shoulder and elbow, and identify areas of dissatisfaction and potential improvement. Between 1995 and 2012, the NHSLA recorded 811 claims related to the shoulder and elbow, 581 of which were settled. This comprised 364 shoulder (64%), and 217 elbow (36%) claims. A total of £18.2 million was paid out in settled claims. Overall diagnosis, mismanagement and intra-operative nerve injury were the most common reasons for litigation. The highest cost paid out resulted from claims dealing with incorrect, missed or delayed diagnosis, with just under £6 million paid out overall. Fractures and dislocations around the shoulder and elbow were common injuries in this category. All 11 claims following wrong-site surgery that were settled led to successful payouts.

This study highlights the diagnoses and procedures that need to be treated with particular vigilance. Having an awareness of the areas that lead to litigation in shoulder and elbow surgery will help to reduce inadvertent risks to patients and prevent dissatisfaction and possible litigation.

Cite this article: Bone Joint J 2014; 96-B:574–9.


The Bone & Joint Journal
Vol. 95-B, Issue 5 | Pages 668 - 672
1 May 2013
Abdel MP Hattrup SJ Sperling JW Cofield RH Kreofsky CR Sanchez-Sotelo J

Instability after arthroplasty of the shoulder is difficult to correct surgically. Soft-tissue procedures and revision surgery using unconstrained anatomical components are associated with a high rate of failure. The purpose of this study was to determine the results of revision of an unstable anatomical shoulder arthroplasty to a reverse design prosthesis. Between 2004 and 2007, 33 unstable anatomical shoulder arthroplasties were revised to a reverse design. The mean age of the patients was 71 years (53 to 86) and their mean follow-up was 42 months (25 to 71). The mean time to revision was 26 months (4 to 164). Pain scores improved significantly (pre-operative visual analogue scale (VAS) of 7.2 (sd 1.6); most recent VAS 2.2 (sd 1.9); p = 0.001). There was a statistically significant increase in mean active forward elevation from 40.2° (sd 27.3) to 97.0° (sd 36.2) (p = 0.001). There was no significant difference in internal (p = 0.93) or external rotation (p = 0.40). Radiological findings included notching in five shoulders (15%) and heterotopic ossification of the inferior capsular region in three (9%). At the last follow-up 31 shoulders (94%) were stable. The remaining two shoulders dislocated at 2.5 weeks and three months post-operatively, respectively. According to the Neer rating system, there were 13 excellent (40%), ten satisfactory (30%) and ten unsatisfactory results (30%). Revision of hemiarthroplasty or anatomical total shoulder replacement for instability using a reverse design prosthesis gives good short-term results.

Cite this article: Bone Joint J 2013;95-B:668–72.


The Bone & Joint Journal
Vol. 95-B, Issue 1 | Pages 70 - 74
1 Jan 2013
Dattani R Smith CD Patel VR

We investigated the incidence of and risk factors for venous thromboembolism (VTE) following surgery of the shoulder and elbow and assessed the role of thromboprophylaxis in upper limb surgery. All papers describing VTE after shoulder and elbow surgery published in the English language literature before 31 March 2012 were reviewed. A total of 14 papers were available for analysis, most of which were retrospective studies and case series. The incidence of VTE was 0.038% from 92 440 shoulder arthroscopic procedures, 0.52% from 42 261 shoulder replacements, and 0.64% from 4833 procedures for fractures of the proximal humerus (open reduction and internal fixation or hemiarthroplasty). The incidence following replacement of the elbow was 0.26% from 2701 procedures. Diabetes mellitus, rheumatoid arthritis and ischaemic heart disease were identified as the major risk factors. The evidence that exists on thromboprophylaxis is based on level III and IV studies, and we therefore cannot make any recommendations on prophylaxis based on the current evidence. It seems reasonable to adopt a multimodal approach that involves all patients receiving mechanical prophylaxis, with chemical prophylaxis reserved for those who are at high risk for VTE. Cite this article: Bone Joint J 2013;95-B:70–4


The Journal of Bone & Joint Surgery British Volume
Vol. 94-B, Issue 10 | Pages 1382 - 1389
1 Oct 2012
Sewell MD Kang SN Al-Hadithy N Higgs DS Bayley I Falworth M Lambert SM

There is little information about the management of peri-prosthetic fracture of the humerus after total shoulder replacement (TSR). This is a retrospective review of 22 patients who underwent a revision of their original shoulder replacement for peri-prosthetic fracture of the humerus with bone loss and/or loose components. There were 20 women and two men with a mean age of 75 years (61 to 90) and a mean follow-up 42 months (12 to 91): 16 of these had undergone a previous revision TSR. Of the 22 patients, 12 were treated with a long-stemmed humeral component that bypassed the fracture. All their fractures united after a mean of 27 weeks (13 to 94). Eight patients underwent resection of the proximal humerus with endoprosthetic replacement to the level of the fracture. Two patients were managed with a clam-shell prosthesis that retained the original components. The mean Oxford shoulder score (OSS) of the original TSRs before peri-prosthetic fracture was 33 (14 to 48). The mean OSS after revision for fracture was 25 (9 to 31). Kaplan-Meier survival using re-intervention for any reason as the endpoint was 91% (95% confidence interval (CI) 68 to 98) and 60% (95% CI 30 to 80) at one and five years, respectively. There were two revisions for dislocation of the humeral head, one open reduction for modular humeral component dissociation, one internal fixation for nonunion, one trimming of a prominent screw and one re-cementation for aseptic loosening complicated by infection, ultimately requiring excision arthroplasty. Two patients sustained nerve palsies. Revision TSR after a peri-prosthetic humeral fracture associated with bone loss and/or loose components is a salvage procedure that can provide a stable platform for elbow and hand function. Good rates of union can be achieved using a stem that bypasses the fracture. There is a high rate of complications and function is not as good as with the original replacement


Bone & Joint Research
Vol. 1, Issue 9 | Pages 210 - 217
1 Sep 2012
Walton JR Murrell GAC

Objectives

The aim of this study was to determine whether there is any significant difference in temporal measurements of pain, function and rates of re-tear for arthroscopic rotator cuff repair (RCR) patients compared with those patients undergoing open RCR.

Methods

This study compared questionnaire- and clinical examination-based outcomes over two years or longer for two series of patients who met the inclusion criteria: 200 open RCR and 200 arthroscopic RCR patients. All surgery was performed by a single surgeon.


The Journal of Bone & Joint Surgery British Volume
Vol. 94-B, Issue 6 | Pages 721 - 728
1 Jun 2012
Goudie EB Murray IR Robinson CM

Dislocation of the shoulder may occur during seizures in epileptics and other patients who have convulsions. Following the initial injury, recurrent instability is common owing to a tendency to develop large bony abnormalities of the humeral head and glenoid and a susceptibility to further seizures. Assessment is difficult and diagnosis may be missed, resulting in chronic locked dislocations with protracted morbidity. Many patients have medical comorbidities, and successful treatment requires a multidisciplinary approach addressing the underlying seizure disorder in addition to the shoulder pathology. The use of bony augmentation procedures may have improved the outcomes after surgical intervention, but currently there is no evidence-based consensus to guide treatment. This review outlines the epidemiology and pathoanatomy of seizure-related instability, summarising the currently-favoured options for treatment, and their results.


The Journal of Bone & Joint Surgery British Volume
Vol. 94-B, Issue 6 | Pages 799 - 804
1 Jun 2012
Hems TEJ Mahmood F

We reviewed 101 patients with injuries of the terminal branches of the infraclavicular brachial plexus sustained between 1997 and 2009. Four patterns of injury were identified: 1) anterior glenohumeral dislocation (n = 55), in which the axillary and ulnar nerves were most commonly injured, but the axillary nerve was ruptured in only two patients (3.6%); 2) axillary nerve injury, with or without injury to other nerves, in the absence of dislocation of the shoulder (n = 20): these had a similar pattern of nerve involvement to those with a known dislocation, but the axillary nerve was ruptured in 14 patients (70%); 3) displaced proximal humeral fracture (n = 15), in which nerve injury resulted from medial displacement of the humeral shaft: the fracture was surgically reduced in 13 patients; and 4) hyperextension of the arm (n = 11): these were characterised by disruption of the musculocutaneous nerve. There was variable involvement of the median and radial nerves with the ulnar nerve being least affected.

Surgical intervention is not needed in most cases of infraclavicular injury associated with dislocation of the shoulder. Early exploration of the nerves should be considered in patients with an axillary nerve palsy without dislocation of the shoulder and for musculocutaneous nerve palsy with median and/or radial nerve palsy. Urgent operation is needed in cases of nerve injury resulting from fracture of the humeral neck to relieve pressure on nerves.


The Journal of Bone & Joint Surgery British Volume
Vol. 94-B, Issue 1 | Pages 16 - 22
1 Jan 2012
Popovic D King GJW

In light of the growing number of elderly osteopenic patients with distal humeral fractures, we discuss the history of their management and current trends. Under most circumstances operative fixation and early mobilisation is the treatment of choice, as it gives the best results. The relative indications for and results of total elbow replacement versus internal fixation are discussed.


The Journal of Bone & Joint Surgery British Volume
Vol. 93-B, Issue 7 | Pages 937 - 941
1 Jul 2011
Bae J Oh J Chon C Oh C Hwang J Yoon Y

We evaluated the biomechanical properties of two different methods of fixation for unstable fractures of the proximal humerus. Biomechanical testing of the two groups, locking plate alone (LP), and locking plate with a fibular strut graft (LPSG), was performed using seven pairs of human cadaveric humeri. Cyclical loads between 10 N and 80 N at 5 Hz were applied for 1 000 000 cycles. Immediately after cycling, an increasing axial load was applied at a rate of displacement of 5 mm/min. The displacement of the construct, maximum failure load, stiffness and mode of failure were compared. The displacement was significantly less in the LPSG group than in the LP group (p = 0.031). All maximum failure loads and measures of stiffness in the LPSG group were significantly higher than those in the LP group (p = 0.024 and p = 0.035, respectively). In the LP group, varus collapse and plate bending were seen. In the LPSG group, the humeral head cut out and the fibular strut grafts fractured. No broken plates or screws were seen in either group. We conclude that strut graft augmentation significantly increases both the maximum failure load and the initial stiffness of this construct compared with a locking plate alone


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 10 | Pages 1397 - 1402
1 Oct 2010
Nada AN Debnath UK Robinson DA Jordan C

We describe the clinical outcome of a technique of surgical augmentation of chronic massive tears of the rotator cuff using a polyester ligament (Dacron) in 21 symptomatic patients (14 men, seven women) with a mean age of 66.5 years (55.0 to 85.0). All patients had MRI and arthroscopic evidence of chronic massive tears. The clinical outcome was assessed using the Constant and Murley and patient satisfaction scores at a mean follow-up of 36 months (30 to 46). The polyester ligament (500 mm × 10 mm) was passed into the joint via the portal of Neviaser, medial to the tear through healthy cuff. The two ends of the ligament holding the cuff were passed through tunnels made in the proximal humerus at the footprint of the insertion of the cuff. The ligament was tied with a triple knot over the humeral cortex. All the patients remained free from pain (p < 0.001) with improvement in function (p < 0.001) and range of movement (p < 0.001). The mean pre-operative and post-operative Constant scores were 46.7 (39.0 to 61.0) and 85.4 (52.0 to 96.0), respectively (p < 0.001). The mean patient satisfaction score was 90%. There were two failures, one due to a ruptured ligament after one year and the other due to deep-seated infection. The MR scan at the final follow-up confirmed intact and thickened bands in 15 of 17 patients. This technique of augmentation gives consistent relief from pain with improved shoulder movement in patients with symptomatic massive tears of the rotator cuff


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 10 | Pages 1403 - 1409
1 Oct 2010
Pape G Zeifang F Bruckner T Raiss P Rickert M Loew M

Fractures of the proximal humerus can lead to malalignment of the humeral head, necrosis and post-traumatic osteoarthritis. In such cases surface replacement might be a promising option. A total of 28 shoulders with glenohumeral arthritis subsequent to a fracture underwent surface replacement arthroplasty of the humeral head in patients with a mean age of 60 years (35 to 83). On the basis of the inclination of the impacted head, post-traumatic arthritis was divided into three types: type 1, an impacted fracture of the head in an anatomical position (seven cases); type 2, a valgus impacted fracture (13 cases); type 3, a varus impacted fracture (eight cases). The outcome was measured by means of the Constant score. According to the Boileau classification of the sequelae of fractures of the proximal humerus, all 28 patients had a final result of intra-capsular category 1. The mean Constant score for the 28 shoulders increased from 23.2 points (2 to 45) pre-operatively to 55.1 points (20 to 89) at a mean of 31 months (24 to 66) post-operatively. Valgus impacted fractures had significantly better results (p < 0.039). Surface replacement arthroplasty can provide good results for patients with post-traumatic osteoarthritis of the shoulder. Their use avoids post-operative complications of the humeral shaft, such as peri-prosthetic fractures. Further surgery can be undertaken more easily as the bone stock is preserved


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 8 | Pages 1107 - 1111
1 Aug 2010
Rees JL Dawson J Hand GCR Cooper C Judge A Price AJ Beard DJ Carr AJ

We have compared the outcome of hemiarthroplasty of the shoulder in three distinct diagnostic groups, using survival analysis as used by the United Kingdom national joint registers, patient-reported outcome measures (PROMs) as recommended by Darzi in the 2008 NHS review, and transition and satisfaction questions.

A total of 72 hemiarthroplasties, 19 for primary osteoarthritis (OA) with an intact rotator cuff, 22 for OA with a torn rotator cuff, and 31 for rheumatoid arthritis (RA), were followed up for between three and eight years. All the patients survived, with no revisions or dislocations and no significant radiological evidence of loosening. The mean new Oxford shoulder score (minimum/worst 0, maximum/best 48) improved significantly for all groups (p < 0.001), in the OA group with an intact rotator cuff from 21.4 to 38.8 (effect size 2.9), in the OA group with a torn rotator cuff from 13.3 to 27.2 (effect size 2.1) and in the RA group from 13.7 to 28.0 (effect size 3.1). By this assessment, and for the survival analysis, there was no significant difference between the groups. However, when ratings using the patient satisfaction questions were analysed, eight (29.6%) of the RA group were ‘disappointed’, compared with one (9.1%) of the OA group with cuff intact and one (7.7%) of the OA group with cuff torn. All patients in the OA group with cuff torn indicated that they would undergo the operation again, compared to ten (90.9%) in the OA group with cuff intact and 20 (76.9%) in the RA group.

The use of revision rates alone does not fully represent outcome after hemiarthroplasty of the shoulder. Data from PROMs provides more information about change in pain and the ability to undertake activities and perform tasks. The additional use of satisfaction ratings shows that both the rates of revision surgery and PROMs need careful interpretation in the context of patient expectations.


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 6 | Pages 811 - 816
1 Jun 2010
Robinson CM Akhtar MA Jenkins PJ Sharpe T Ray A Olabi B

Displaced fractures of the lateral end of the clavicle in young patients have a high incidence of nonunion and a poor functional outcome after conservative management. Operative treatment is therefore usually recommended. However, current techniques may be associated with complications which require removal of the fixation device. We have evaluated the functional and radiological outcomes using a novel technique of open reduction and internal fixation. A series of 16 patients under 60 years of age with displaced fractures of the lateral end were treated by open reduction and fixation using a twin coracoclavicular endobutton technique. They were followed up for the first year after their injury.

At one year the mean Constant score was 87.1 and the median Disabilities of the Arm, Shoulder and Hand score was 3.3. All fractures had united, except in one patient who developed an asymptomatic fibrous union. One patient had post-traumatic stiffness of the shoulder, which resolved with physiotherapy. None required re-operation.

This technique produces good functional and radiological outcomes with a low prevalence of complications and routine implant removal is not necessary.


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 4 | Pages 535 - 539
1 Apr 2010
Cazeneuve JF Cristofari D

We have previously described the short-term outcome of the use of reverse shoulder arthroplasty in the treatment of acute complex proximal humeral fractures in the elderly. We now report the clinical and radiological outcome of 36 fractures at a mean of 6.6 years (1 to 16). Previously, at a mean follow-up of 6 years (1 to 12) the mean Constant score was 58.5; this was reduced to 53 points with the further follow-up. A total of 23 patients (63%) had radiological evidence of loosening of the glenoid component. Nevertheless, only one patient had aseptic loosening of the baseplate at 12 years’ follow-up.

The reduction in the mean Constant score with longer follow-up and the further development of scapular notching is worrying.

New developments in design, bearing surfaces and surgical technique, and further follow-up, will determine whether reverse shoulder arthroplasty has a place in the management of complex proximal humeral fractures in the elderly.


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 3 | Pages 387 - 392
1 Mar 2010
Kasten P Pape G Raiss P Bruckner T Rickert M Zeifang F Loew M

We have investigated the mid-term outcome of total shoulder replacement using a keeled cemented glenoid component and a modern cementing technique with regard to the causes of failure and loosening of the components.

Between 1997 and 2003 we performed 96 total shoulder replacements on 88 patients, 24 men and 64 women with a mean age of 69.7 years (31 to 82). The minimum follow-up was five years and at the time of review 87 shoulders (77 patients) were examined at a mean follow-up of 89.1 months (60 to 127). Cumulative survival curves were generated with re-operations (accomplished and planned), survivorship of the proshesis, loosening of the glenoid (defined as tilt > 5° or subsidence > 5 mm), the presence of radiolucent lines and a Constant score of < 30 as the endpoints.

There were two re-operations not involving revision of the implants and the survival rate of the prosthesis was 100.0% for the follow-up period, with an absolute Constant score of > 30 as the endpoint the survival rate was 98%. Radiological glenoid loosening was 9% after five years, and 33% after nine years. There was an incidence of 8% of radiolucent lines in more than three of six zones in the immediate post-operative period, of 37.0% after the first year which increased to 87.0% after nine years. There was no correlation between the score of Boileau and the total Constant score at the latest follow-up, but there was correlation between glenoid loosening and pain (p = 0.001).

We found that total shoulder replacement had an excellent mid-term survivorship and clinical outcome. The surgical and cementing techniques were related to the decrease in radiolucent lines around the glenoid compared with earlier studies. One concern, however, was the fact that radiolucent lines increased over time and there was a rate of glenoid loosening of 9% after five years and 33% after nine years. This suggests that the design of the glenoid component, and the implantation and cementing techniques may need further improvement.


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 1 | Pages 83 - 91
1 Jan 2010
Moosmayer S Lund G Seljom U Svege I Hennig T Tariq R Smith H

In order to compare the outcome from surgical repair and physiotherapy, 103 patients with symptomatic small and medium-sized tears of the rotator cuff were randomly allocated to one of the two approaches. The primary outcome measure was the Constant score, and secondary outcome measures included the self-report section of the American Shoulder and Elbow Surgeons score, the Short Form 36 Health Survey and subscores for shoulder movement, pain, strength and patient satisfaction. Scores were taken at baseline and after six and 12 months by a blinded assessor. Nine patients (18%) with insufficient benefit from physiotherapy after at least 15 treatment sessions underwent secondary surgical treatment.

Analysis of between-group differences showed better results for the surgery group on the Constant scale (difference 13.0 points, p − 0.002), on the American Shoulder and Elbow surgeons scale (difference 16.1 points, p < 0.0005), for pain-free abduction (difference 28.8°, p = 0.003) and for reduction in pain (difference on a visual analogue scale −1.7 cm, p < 0.0005).


The Journal of Bone & Joint Surgery British Volume
Vol. 92-B, Issue 1 | Pages 71 - 76
1 Jan 2010
Diklic ID Ganic ZD Blagojevic ZD Nho SJ Romeo AA

The treatment of a chronic posterior dislocation of the shoulder is often determined by the size of the associated impression fracture of the humeral head. Our hypothesis was that patients with a chronic unreduced posterior dislocation of the shoulder and a defect in the humeral head involving between 25% to 50% of the articular surface, would do better if reconstructed with an allograft from the femoral head rather than treated by a non-anatomical reconstruction. We reviewed ten men and three women with a mean age of 42 years (36 to 51) at a mean follow-up of 54 months (41 to 64) who had this procedure. At follow-up, nine had no pain or restriction of activities of daily living. Their mean Constant-Murley shoulder score was 86.8 (43 to 98). No patient had symptoms of instability of the shoulder.

Reconstruction of the defect in the humeral head with an allograft provides good pain relief, stability and function for patients with a locked, chronic posterior dislocation where the defect involves between 25% and 50% of the circumference of the articular surface.