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The Bone & Joint Journal
Vol. 100-B, Issue 3 | Pages 338 - 345
1 Mar 2018
Watkins CEL Elson DW Harrison JWK Pooley J

Aim

The aim of this study was to report the long-term outcome and implant survival of the lateral resurfacing elbow (LRE) arthroplasty in the treatment of elbow arthritis.

Patients and Methods

We reviewed a consecutive series of 27 patients (30 elbows) who underwent LRE arthroplasty between December 2005 and January 2008. There were 15 women and 12 men, with a mean age of 61 years (25 to 82). The diagnosis was primary hypotrophic osteoarthritis (OA) in 12 patients (14 elbows), post-traumatic osteoarthritis (PTOA) in five (five elbows) and rheumatoid arthritis (RA) in ten patients (11 elbows). The mean clinical outcome scores including the Mayo Elbow Performance Score (MEPS), the American Shoulder and Elbow Surgeons elbow score (ASES-e), the mean range of movement and the radiological outcome were recorded at three, six and 12 months and at a mean final follow-up of 8.3 years (7.3 to 9.4). A one sample t-test comparing pre and postoperative values, and survival analysis using the Kaplan–Meier method were undertaken.


The Journal of Bone & Joint Surgery British Volume
Vol. 94-B, Issue 3 | Pages 308 - 314
1 Mar 2012
Ito H Tanino H Yamanaka Y Nakamura T Takahashi D Minami A Matsuno T

We have previously described the mid- to long-term results of conventional simple varus intertrochanteric osteotomy for osteonecrosis of the femoral head, showing that 19 of the 26 hips had good or excellent results. We extended the follow-up to a mean of 18.1 years (10.5 to 26) including a total of 34 hips in 28 patients, with a mean age at surgery of 33 years (19 to 53). There were 18 men and ten women and 25 hips (74%) had a satisfactory result with a Harris hip score ≥ 80. In all, six hips needed total hip replacement (THR) or hemiarthroplasty. The collapse of the femoral head or narrowing of the joint space was found to have progressed in nine hips (26%). Leg shortening after osteotomy was a mean of 19 mm (8 to 36). With conversion to THR or hemiarthroplasty as the endpoint, the ten-year survival rate was 88.2% (95% confidence interval (CI) 82.7 to 93.7) and the 20-year survival rate was 79.7% (95% CI 72.1 to 87.3); four hips were converted at ten years and other two hips were converted at 20 years.

Shortening of the leg after osteotomy remains a concern; however, the conventional varus half-wedge osteotomy provides favourable long-term results in hips with less than two-thirds of the medial part of the femoral head affected by necrotic bone and with normal bone superolaterally.


The Bone & Joint Journal
Vol. 104-B, Issue 9 | Pages 1095 - 1100
1 Sep 2022
McNally MA Ferguson JY Scarborough M Ramsden A Stubbs DA Atkins BL

Aims. Excision of chronic osteomyelitic bone creates a dead space which must be managed to avoid early recurrence of infection. Systemic antibiotics cannot penetrate this space in high concentrations, so local treatment has become an attractive adjunct to surgery. The aim of this study was to present the mid- to long-term results of local treatment with gentamicin in a bioabsorbable ceramic carrier. Methods. A prospective series of 100 patients with Cierny-Mader Types III and IV chronic ostemyelitis, affecting 105 bones, were treated with a single-stage procedure including debridement, deep tissue sampling, local and systemic antibiotics, stabilization, and immediate skin closure. Chronic osteomyelitis was confirmed using strict diagnostic criteria. The mean follow-up was 6.05 years (4.2 to 8.4). Results. At final follow-up, six patients (six bones) had recurrent infection; thus 94% were infection-free. Three infections recurred in the first year, two in the second year, and one 4.5 years postoperatively. Recurrence was not significantly related to the physiological class of the patient (1/20 Class A (5%) vs 5/80 Class B (6.25%); p = 0.833), nor was it significantly related to the aetiology of the infection, the organisms which were cultured or the presence of nonunion before surgery (1/10 with nonunion (10%) vs 5/90 without nonunion (5.6%); p = 0.570). Organisms with intermediate or high-grade resistance to gentamicin were significantly more likely in polymicrobial infections (9/21; 42.8%) compared with monobacterial osteomyelitis (7/79 (8.9%); p < 0.001). However, recurrence was not significantly more frequent when a resistant organism was present (1/16 for resistant cases (6.25%) vs 5/84 in those with a microbiologically sensitive infection (5.95%); p = 0.958). Conclusion. We found that a single-stage protocol, including the use of a high-delivery local antibiotic ceramic carrier, was effective over a period of several years. The method can be used in a wide range of patients, including those with significant comorbidities and an infected nonunion. Cite this article: Bone Joint J 2022;104-B(9):1095–1100


The Bone & Joint Journal
Vol. 100-B, Issue 7 | Pages 953 - 956
1 Jul 2018
Erşen A Atalar AC Bayram S Demirel M Tunalı O Demirhan M

Aims. The present study aimed to investigate the long-term functional results of scapulothoracic fusion using multifilament cables in patients with facioscapulohumeral dystrophy (FSHD) to identify if the early improvement from this intervention is maintained. Patients and Methods. We retrospectively investigated the long-term outcomes of 13 patients with FSHD (18 shoulders) in whom scapulothoracic fusion using multifilament cables was performed between 2004 and 2007. These patients have previously been reported at a mean of 35.5 months (24 to 87). There were eight men and five women with a mean age of 26 years. Their mean length of follow-up of our current study was 128 months (94 to 185). To evaluate long-term functional results, the range of shoulder flexion and abduction, Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) scores were analyzed with a comparison of preoperatively, interim and at the final outcomes. The fusion was examined radiographically in all. Results. The complication rate was 33% (six of 18 scapulothoracic fusions) in 13 patients, which comprised failure of fusion in four shoulders (four patients) all occurring within the first year postoperatively. In two shoulders (one patient) wound problems arose due to attribution from the cables which required shortening but the fusion developed satisfactorily. At the final examination, the mean QuickDASH score and range of movement significantly improved in all but one patient (p < 0.001, p < 0.001 and p < 0.001). In the comparison of 13 patients’ mid- and long-term results, the mean QuickDASH score decreased from 9.8 (. sd. 6.7; 3 to 26) in the third year to 9.1 (. sd. 5.6; 3 to 22) in the tenth year (p = 0.7); the mean range of shoulder flexion and abduction decreased from 129° (. sd. 22°; 90° to 160°) and 124° (. sd. 12; 100° to 150°) at the mid-term to 103° (. sd. 12°; 80° to 120°) and 101° (. sd. 8°; 80° to 120°) at the long-term, respectively (p = 0.78 and p = 0.65). Conclusion. Scapulothoracic fusion using a multiple cabling method can confer a considerable improvement in clinical and functional outcomes for most patients with FSHD after a long follow-up period. The technique requires careful execution to avoid complications. Cite this article: Bone Joint J 2018;100-B:953–6


The Bone & Joint Journal
Vol. 100-B, Issue 11 | Pages 1499 - 1454
1 Nov 2018
Green CM Buckley SC Hamer AJ Kerry RM Harrison TP

Aims. The management of acetabular defects at the time of revision hip arthroplasty surgery is a challenge. This study presents the results of a long-term follow-up study of the use of irradiated allograft bone in acetabular reconstruction. Patients and Methods. Between 1990 and 2000, 123 hips in 110 patients underwent acetabular reconstruction for aseptic loosening, using impaction bone grafting with frozen, irradiated, and morsellized femoral heads and a cemented acetabular component. A total of 55 men and 55 women with a mean age of 64.3 years (26 to 97) at the time of revision surgery are included in this study. Results. At a mean follow-up of 16.9 years, there had been 23 revisions (18.7%), including ten for infection, eight for aseptic loosening, and three for dislocation. Of the 66 surviving hips (58 patients) that could be reassessed, 50 hips (42 patients; 75.6%) were still functioning satisfactorily. Union of the graft had occurred in all hips with a surviving implant. Survival analysis for all indications was 80.6% at 15 years (55 patients at risk, 95% confidence interval (CI) 71.1 to 87.2) and 73.7% at 20 years (eight patients at risk, 95% CI 61.6 to 82.5). Conclusion. Acetabular reconstruction using frozen, irradiated, and morsellized allograft bone and a cemented acetabular component is an effective method of treatment. It gives satisfactory long-term results and is comparable to other types of reconstruction. Cite this article: Bone Joint J 2018;100-B:1449–54


The Bone & Joint Journal
Vol. 102-B, Issue 1 | Pages 64 - 71
1 Jan 2020
Tsuda Y Fujiwara T Stevenson JD Parry MC Tillman R Abudu A

Aims. The purpose of this study was to report the long-term results of extendable endoprostheses of the humerus in children after the resection of a bone sarcoma. Methods. A total of 35 consecutive patients treated with extendable endoprosthetic replacement of the humerus in children were included. There were 17 boys and 18 girls in the series with a median age at the time of initial surgery of nine years (interquartile range (IQR) 7 to 11). Results. The median follow-up time was 10.6 years (IQR 3.9 to 20.4). The overall implant survival at ten years was 75%. Complications occurred in 13 patients (37%). Subluxation at the proximal humerus occurred in 19 patients (54%) but only six (17%) were symptomatic. Subluxation was seen more commonly in children under the age of nine years (86%) than in those aged nine years or more (33%) (p = 0.002). Implant failure occurred in nine patients (26%): the most common cause was aseptic loosening (four patients, 11%). Lengthening of the implant was carried out in 23 patients (66%). At final follow up, three patients had a limb that was shortened by 5 cm or more. The mean Musculoskeletal Tumor Society (MSTS) functional score was 79% (73% to 90%). Conclusion. Extendable endoprosthetic replacement is a reliable method of reconstructing humerus after excision of a bone sarcoma. Children who are less than nine years old have a high risk of subluxation. Cite this article: Bone Joint J 2020;102-B(1):64–71


The Journal of Bone & Joint Surgery British Volume
Vol. 85-B, Issue 6 | Pages 836 - 840
1 Aug 2003
Kooijman HJ Driessen APPM van Horn JR

We studied retrospectively the outcome of patellofemoral arthroplasty (PFA) using the Richards prosthesis in 51 patients (56 knees). Their mean age was 50 years (30 to 77). In 43 patients (45 knees), the American Knee Society score and the patients’ subjective judgement were assessed. Excellent or good results were obtained in 86% of cases at a mean follow-up of 17 years (15 to 21). Because of ongoing tibiofemoral osteoarthritis, two patients required a high tibial osteotomy and ten PFAs were converted to a total knee arthroplasty after a mean of 15.6 years (10 to 21). The PFAs were stable during follow-up with a loosening rate of only 2%. We conclude that a patellofemoral prosthesis is a good treatment option with successful long-term results in middle-aged patients with radiologically documented, isolated, patellofemoral osteoarthritis


The Journal of Bone & Joint Surgery British Volume
Vol. 83-B, Issue 3 | Pages 355 - 358
1 Apr 2001
Gill GS Joshi AB

We present the long-term results of the Kinematic Condylar Knee Arthroplasty followed in a prospective fashion. Between October 1982 and March 1988, 404 consecutive replacement arthroplasties were carried out on 335 patients. Of these, 354 knees had osteoarthritis, 45 rheumatoid arthritis and five other diagnoses. At the time of final follow-up 158 patients (188 knees) had died. No patient was lost to follow-up. The minimum follow-up for all living patients was ten years (10 to 17). The mean age at surgery was 68 years (30 to 92). There were seven complications (1.7%). Sixteen knees (3.9%) were revised, four because of infection. Survivorship was 99.4% (CI 97.9 to 99.8) at five years, 98.2% (CI 96.1 to 99.2) at ten years and 92.6% (CI 87.6 to 95.6) at 17 years


The Journal of Bone & Joint Surgery British Volume
Vol. 80-B, Issue 1 | Pages 70 - 77
1 Jan 1998
Hansson G Billing L Högstedt B Jerre R Wallin J

We reviewed the radiological and clinical long-term results after the nailing in situ of slipped upper femoral epiphysis in 59 hips in 43 patients. The displacement of the epiphysis had been measured as the ‘slipping angle’ before operation and related to the results at follow-up at a mean of 30.9 years (27 to 34). The mean age at follow-up was 44.2 years (39 to 50). Radiographic re-examination of 41 hips with slipping angles of ≤30° at the time of operation showed that eight (20%) had developed mild osteoarthritis and one had severe changes. For 18 hips with slipping angles ranging from 31 to 50° at surgery six (33%) had mild osteoarthritis and three had severe changes. The differences did not quite achieve statistical significance (p = 0.09). Clinical re-examination of the 41 hips with slipping angles of ≤30° showed fair or poor results (Harris hip score < 90) in three (7%). In the 18 hips with slipping of 31 to 50°, four had fair or poor results (22%) (p= 0.13). We conclude that nailing in situ for slipping of ≤30°, using one thin nail, can give excellent long-term results. At present we recommend that hips with slips ranging from 31 to 50° should also be nailed in situ, but further long-term studies are required, especially on the choice between nailing in situ and corrective osteotomy for slips in excess of 50°


The Journal of Bone & Joint Surgery British Volume
Vol. 90-B, Issue 1 | Pages 27 - 30
1 Jan 2008
Rajaratnam SS Jack C Tavakkolizadeh A George MD Fletcher RJ Hankins M Shepperd JAN

Between 1986 and 1991 we implanted 331 consecutive Furlong hydroxyapatite-coated femoral components of a total hip replacement in 291 patients. A cemented acetabular prosthesis was used in 217 hips and a hydroxyapatite-coated component in 114. We describe the long-term clinical and radiological survival of the femoral component at a mean follow-up of 17.5 years (15 to 21). Only two patients (0.68%) were lost to follow-up. With revision of the femoral component for any reason as the endpoint, the survival at a mean of 17 years was 97.4% (95% confidence interval 94.1 to 99.5), and with revision for aseptic loosening as the endpoint it was 100%. The survival at a maximum of 21 years with revision of the femoral component for any reason as the endpoint was 97.4% (95% confidence interval 81.0 or 99.5). These results compare favourably with the best long-term results of cemented or uncemented femoral components used in total hip replacement


The Journal of Bone & Joint Surgery British Volume
Vol. 93-B, Issue 8 | Pages 1088 - 1092
1 Aug 2011
Lizaur A Sanz-Reig J Gonzalez-Parreño S

The purpose of this study was to review the long-term outcomes of a previously reported prospective series of 46 type III acromioclavicular dislocations. These were treated surgically with temporary fixation of the acromioclavicular joint with wires, repair of the acromioclavicular ligaments, and overlapped suture of the deltoid and trapezius muscles. Of the 46 patients, one had died, four could not be traced, and three declined to return for follow-up, leaving 38 patients in the study. There were 36 men and two women, with a mean age at follow-up of 57.3 years (41 to 71). The mean follow-up was 24.2 years (21 to 26). Patients were evaluated using the Imatani and University of California, Los Angeles (UCLA) scoring systems. Their subjective status was assessed using the Disabilities of the Arm, Shoulder and Hand and Simple Shoulder Test questionnaires, and a visual analogue scale for patient satisfaction. The examination included radiographs of the shoulder. At a follow-up of 21 years, the results were satisfactory in 35 (92.1%) patients and unsatisfactory in three (7.9%). In total, 35 patients (92.1%) reported no pain, one slight pain, and two moderate pain. All except two patients had a full range of shoulder movement compared with the opposite side. Unsatisfactory results were the result of early redisplacement in two patients, and osteoarthritis without redisplacement in one. According to the Imatani and UCLA scores, there was no difference between the operated shoulder and the opposite shoulder (p > 0.05). Given the same situation, 35 (92.1%) patients would opt for the same surgical treatment again. Operative treatment of type III acromioclavicular joint injuries produces satisfactory long-term results


The Journal of Bone & Joint Surgery British Volume
Vol. 82-B, Issue 6 | Pages 824 - 829
1 Aug 2000
Morita S Yamamoto H Hasegawa S Kawachi S Shinomiya K

We treated 31 hips in 30 patients with advanced osteoarthritis of the hip secondary to acetabular dysplasia, by valgus-extension femoral osteotomy. The mean follow-up was 12.7 years (10 to 17). Acetabuloplasty was added in ten severely dysplastic hips. In 28 hips, radiological widening of the joint space was seen three years after operation, but in 12 had narrowed again by ten years. Survivorship analysis showed that the rate of survival was 82% using the pain score as the index of failure, and 72% based on radiological findings at ten years. Better long-term results were obtained in hips which had an acetabular head index greater than 70% or a roof osteophyte more than 5 mm in length three years after operation. Acetabuloplasty should be added for the hip which is severely dysplastic and with a poorly developed roof osteophyte


The Journal of Bone & Joint Surgery British Volume
Vol. 68-B, Issue 1 | Pages 111 - 116
1 Jan 1986
Walker S Sharma P Parr N Cavendish M

We have reviewed 105 Liverpool Mark II knee replacements in 71 patients to assess survival and long-term results. Assessment was both clinical and radiological, using a modification of the British Orthopaedic Association knee function assessment chart, and analysis was by the survivorship method as advocated by Tew and Waugh. The follow-up period was between 13 and 113 months with 42 prostheses being in situ for over six years. Eight knees (7.6%) have been revised or arthrodesed because of infection or loosening, giving a cumulative success rate of 89% after seven years based on prosthesis survival alone. Of the remaining knees, 71.1% were either free of pain or caused only minimal pain. The cumulative success rate as judged by the stricter criteria of the prosthesis being in situ and causing little or no pain suggested a 50% survival between 73 and 96 months. Most patients (77.3%) were enthusiastic or satisfied with their results. Complications included deep wound infection (8.6%), and loosening which needed further surgery (11.4%)


The Journal of Bone & Joint Surgery British Volume
Vol. 65-B, Issue 1 | Pages 43 - 46
1 Jan 1983
Johnson Kirwan E

The long-term results of 17 patients who had had fusion in situ for severe lumbosacral spondylolisthesis are reported. The average follow-up was 14 years with a range of 7 to 20 years. The average age at operation was 16 years. At follow-up seven patients had occasional backache but only one patient had changed his job and no patient had lost any time off work in the previous year. Nine patients felt that their deformity had been improved and all but one patient still rated the results as excellent up to 20 years after the operation. Although all the patients had persistent foreshortening of the trunk only two patients were aware of any cosmetic deformity. There had been no significant increase in forward slip since the previous follow-up examination five years after the operation. There were no late complications nor significant degenerative changes in the lumbar spine. It is concluded that although fusion in situ does little to improve cosmesis very few patients complain about their appearance and that it is a safe and reliable method of treatment for severe spondylolisthesis which has stood the test of time


The Journal of Bone & Joint Surgery British Volume
Vol. 93-B, Issue 11 | Pages 1487 - 1492
1 Nov 2011
Macheras GA Kateros K Galanakos SP Koutsostathis SD Kontou E Papadakis SA

We report the long-term results of the management of neglected chronically infected total knee replacements with a two-stage re-implantation protocol. In 18 of 34 patients (53%) a resistant organism was isolated. All cases were treated by the same surgical team in a specialist centre and had a mean follow-up of 12.1 years (10 to 14). They were evaluated clinically and radiologically using the Knee Society Score (KSS) and the American Knee Society Roentgenographic scoring system, respectively. One patient died after eight years from an unrelated cause and two were lost to follow-up. Three patients (8.8%) developed a recurrent infection for which further surgery was required. The infection was eradicated successfully in 31 patients (91.1%). There was one case of aseptic loosening after 13 years. We found a significant improvement in the KSS at final follow-up (p < 0.001)


The Journal of Bone & Joint Surgery British Volume
Vol. 73-B, Issue 1 | Pages 96 - 99
1 Jan 1991
Korkala O Tanskanen P Makijarvi J Sorvali T Ylikoski M Haapala J

We studied the late outcome of 40 ankles (from a consecutive series of 42) treated by a modified Evans procedure. The peroneus brevis tendon was used to fashion a static tenodesis. All the patients had suffered from persistent lateral instability following an ankle sprain. The follow-up period was between nine and 12 years. Excellent or good results were achieved in 33 ankles (82.5%), three had a fair result, and four were poor. The clinical results were matched by the radiographic results which showed significant talar tilt or anterior talar translation in only three ankles. The functional result showed no positive correlation with the stress-radiographic analysis. We concluded that this modification of the Evans operation gives satisfactory long-term results, which show little change from the good results at 24 to 35 months reported in an earlier paper from our department


The Journal of Bone & Joint Surgery British Volume
Vol. 77-B, Issue 1 | Pages 42 - 49
1 Jan 1995
Fairbank A Bhatia D Jinnah R Hungerford D

We have studied the long-term results of core decompression as the sole treatment for Ficat stages I, II and III ischaemic necrosis of 128 femoral heads in 90 patients. The 5-, 10- and 15-year survival rates for the three stages were respectively: stage I 100%, 96% and 90%; stage II 85%, 74% and 66%; and stage III 58%, 35% and 23%. At a mean follow-up of 11 years (4.5 to 19), 55 hips had failed (43%). No further surgery had been needed for 88% of stage-I, 72% of stage-II and 26% of stage-III hips; but despite the generally satisfactory clinical results, 56% of the hips had progressed radiographically by at least one Ficat stage. Complications of the core procedure included four fractures, all from postoperative falls, and one head perforation due to technical error. We conclude that core decompression delays the need for total hip replacement in young patients with ischaemic necrosis


The Journal of Bone & Joint Surgery British Volume
Vol. 87-B, Issue 5 | Pages 623 - 627
1 May 2005
Kim Y

Between January 1984 and January 1986, 131 porous-coated anatomic total hip replacements were performed in 119 consecutive patients. Of these, 100 patients (110 hips) who were alive at a minimum of 18 years after replacement were included in the study. The mean age of the patients at surgery was 48.4 years and that of surviving patients at the latest follow-up was 67.8 years. The mean duration of the clinical and radiological follow-up was 19.4 years (18 to 20). The mean Harris hip score initially improved from 55 points before to 95 points at two years after operation, but subsequently decreased to 91 points after six years, 87 points after 11.2 years, and 85 points after 19.4 years. At the final follow-up, 23 hips (18%) of the entire cohort and 21% of survivors had undergone revision because of loosening or osteolysis of the acetabular component and eight hips (6%) of the entire cohort and 7% of survivors for loosening or osteolysis of the femoral component. Only four femoral components (4%) were revised for isolated aseptic loosening without osteolysis and two (2%) for recurrent dislocation. On the basis of these long-term results, the porous-coated anatomic femoral component survived for a minimum of 18 years after operation while the acetabular component was less durable. The findings identify the principles of uncemented joint replacement which can be applied to current practice


The Bone & Joint Journal
Vol. 101-B, Issue 6_Supple_B | Pages 123 - 126
1 Jun 2019
El-Husseiny M Masri B Duncan C Garbuz DS

Aims

We investigated the long-term performance of the Tripolar Trident acetabular component used for recurrent dislocation in revision total hip arthroplasty. We assessed: 1) rate of re-dislocation; 2) incidence of complications requiring re-operation; and 3) Western Ontario and McMaster Universities osteoarthritis index (WOMAC) pain and functional scores.

Patients and Methods

We retrospectively identified 111 patients who had 113 revision tripolar constrained liners between 1994 and 2008. All patients had undergone revision hip arthroplasty before the constrained liner was used: 13 after the first revision, 17 after the second, 38 after the third, and 45 after more than three revisions. A total of 75 hips (73 patients) were treated with Tripolar liners due to recurrent instability with abductor deficiency, In addition, six patients had associated cerebral palsy, four had poliomyelitis, two had multiple sclerosis, two had spina bifida, two had spondyloepiphyseal dysplasia, one had previous reversal of an arthrodesis, and 21 had proximal femoral replacements. The mean age of patients at time of Tripolar insertions was 72 years (53 to 89); there were 69 female patients (two bilateral) and 42 male patients. All patients were followed up for a mean of 15 years (10 to 24). Overall, 55 patients (57 hips) died between April 2011 and February 2018, at a mean of 167 months (122 to 217) following their tripolar liner implantation. We extracted demographics, implant data, rate of dislocations, and incidence of other complications.


The Journal of Bone & Joint Surgery British Volume
Vol. 83-B, Issue 4 | Pages 510 - 512
1 May 2001
Gill GS Joshi AB

We analysed the long-term results with a mean follow-up of 10.2 years, of 66 total knee replacements in 42 patients with rheumatoid arthritis. In all cases the posterior cruciate ligament was retained. There were only three complications (4.5%). Revision surgery was necessary in five knees (7.6%), including one (1.5%) with infection. At the final follow-up, 75.8% of knees were rated excellent clinically. Only 15% had an excellent function score. The survival rate of the implant was 90.7% at 19 years. The clinical, radiological and survivorship analysis shows that the posterior-cruciate-retaining knee arthroplasty performs well in rheumatoid arthritis