Correlation of histological and microbiological findings in septic and aseptic knee implant failure.

INTRODUCTION: The Musculoskeletal Infection Society (MSIS) has defined specific clinical and laboratory criteria for the diagnosis of periprosthetic joint infection (PJI). In this study we assessed the diagnostic utility of MSIS microbiological and histological criteria for PJI in 138 cases of septic and aseptic knee implant failure. MATERIALS AND METHODS: Intra-operative samples from 60 cases of knee septic implant failure (SIF) and 78 cases of aseptic implant failure (AIF), defined on the basis of clinical, laboratory and operative findings/surgical management, were analysed microbiologically and histologically. Findings were correlated with the final clinical diagnosis and the specificity, sensitivity, accuracy, positive and negative predictive value of MSIS microbiological and histological criteria for knee PJI were assessed. RESULTS: 80% of SIF cases showed culture of the same organism from two or more samples (ie MSIS microbiological criteria for definite PJI); 8.3% grew an organism from one sample, and 11.7% showed no growth from any sample. 23.1% of AIF cases grew an organism from one sample and 76.9% showed no growth from any sample. MSIS histological criteria for PJI identified 96.7% of SIF cases. The sensitivity, specificity, accuracy and positive and negative predictive value of MSIS histological criteria for PJI were 96.7%, 100%, 98.6%, 100% and 97.5%, respectively. MSIS microbiological and histological criteria identified all AIF cases. CONCLUSIONS: Knee PJI is more often identified by current MSIS histological than microbiological criteria. A significant proportion of SIF cases show either no growth or growth of an organism from only one sample. AIF is identified by both MSIS microbiological and histological criteria. Correlation of clinical, radiological and laboratory findings is required for the diagnosis of knee PJI.

Cementless fixation in medial unicompartmental knee arthroplasty: a systematic review.

PURPOSE: The aim of this study was to evaluate clinical outcome, failures, implant survival, and complications encountered with cementless fixation in unicompartmental knee arthroplasty (UKA). METHODS: A systematic review of the literature on cementless fixation in UKA was performed according to the PRISMA guidelines. The following database was comprehensively searched: PubMed, Cochrane, Medline, CINAHL, Embase, and Google Scholar. The keywords "unicompartmental", "unicondylar", "partial knee arthroplasty", and "UKA" were combined with each of the keyword "uncemented", "cementless" and "survival", "complications", and "outcome". The following data were extracted: demographics, clinical outcome, details of failures and revisions, cumulative survival, and complications encountered. The risk of bias of each study was estimated with the MINORS score and a further scoring system based on the presence of the primary outcomes. RESULTS: From a cohort of 63 studies identified using the above methodology, 10 papers (1199 knees) were included in the final review. The mean follow-up ranged from 2 to 11 years (median 5 years). The 5-year survival ranged from 90 to 99 % and the 10-year survival from 92 to 97 %. There were 48 revisions with an overall revision rate of 0.8 per 100 observed component-years. The most common cause of failure was progression of osteoarthritis in the retained compartment (0.9 %). The cumulative incidence of complications and revisions was comparable to that reported in similar studies on cemented UKAs. The advantages of cementless fixation include faster surgical time, avoidance of cementation errors, and lower incidence of radiolucent lines. CONCLUSIONS: Cementless fixation is a safe and effective alternative to cementation in medial UKA. Clinical outcome, failures, reoperation rate, and survival are similar to those reported for cemented implants with lower incidence of radiolucent lines. LEVEL OF EVIDENCE: IV.

Lateral unicompartmental knee replacement for the treatment of arthritis progression after medial unicompartmental replacement.

PURPOSE: Lateral progression of arthritis following medial unicompartmental knee arthroplasty (UKA), although infrequent, is still the most common reason for revision surgery. Treatment options normally include conversion to total knee arthroplasty. An alternative strategy for some patients may be addition of a lateral UKA. We report the first results of staged bi-compartmental UKA (Bi-UKA) strategy. METHODS: We retrospectively selected from our UKA database patients who underwent a lateral UKA to treat a symptomatic lateral osteoarthritis progression after a medial UKA. The analysis included a clinical and radiological assessment of each patient. RESULTS: Twenty-five patients for a total of 27 knees of staged Bi-UKA were carried out in a single centre. The mean time interval between primary medial UKA and the subsequent lateral UKA was 8.1 years (SD ± 4.6 years). The mean age at the time of the Bi-UKA was 77.1 years (SD ± 6.5 years). The median hospital stay was 3 (range 2-9 days) days, and the mean follow-up after Bi-UKA was 4 years (SD ± 1.9 years). The functional scores showed a significant improvement as compared to the pre-operative status (paired t test, p = 0.003). There were no radiological evidences of failure. None of the patients needed blood transfusion, and there was no significant complications related to the surgical procedure without further surgeries or revisions at final follow-up. CONCLUSIONS: These results suggest that addition of a lateral UKA for arthritis progression following medial UKA is a good option in appropriately selected patients. LEVEL OF EVIDENCE: Observational study without controls, Level IV.

Five-year experience of cementless Oxford unicompartmental knee replacement.

PURPOSE: Cementless unicompartmental knee replacement (UKR) was introduced to address some of the problems that can occur following cemented UKR. The aim of this study was to report the 5-year experience of the first 512 medial cementless Oxford UKR implanted by two surgeons for the recommended indications. METHODS: The first consecutive 512 cementless Phase 3 Oxford UKRs implanted by two surgeons for the recommended indications between June 2004 and October 2013 were prospectively identified and followed up independently. All the procedures were carried out through a minimally invasive approach without eversion or dislocation of the patella. Patients were assessed clinically pre-operatively and at 1, 2, 5, 7 and 10 years after surgery with functional outcome scores and radiographs. RESULTS: There were eight reoperations of which six were revisions giving a 5-year survival of 98 % (95 % CI 94-100 %). At a mean follow-up of 3.4 years (1.0-10.2), the mean OKS was 43 (SD 7), AKSS (objective) was 81 (SD 13), and AKSS (functional) was 86 (SD 17). The first 120 cases had a minimum follow-up of 5 years (mean 5.9; range 5-10.2). In these patients, the mean OKS was 41 (SD 8), AKSS (objective) was 81 (SD 14), and AKSS (functional) was 82 (SD 18). There were no femoral radiolucencies and no complete tibial radiolucencies. 11 % of tibial components had partial radiolucent lines; the remaining 89 % had no radiolucencies. CONCLUSION: The clinical results are as good as or better than those previously reported for cemented fixation. The radiographic results are better with secure bony attachment to the implants in every case. LEVEL OF EVIDENCE: IV.

Comparison of outcomes after UKA in patients with and without chondrocalcinosis: a matched cohort study.

PURPOSE: Chondrocalcinosis can be associated with an inflammatory arthritis and aggressive joint destruction. There is uncertainty as to whether chondrocalcinosis represents a contraindication to unicompartmental knee arthroplasty (UKA). This study reports the outcome of a consecutive series of patients with chondrocalcinosis and medial compartment osteoarthritis treated with UKA matched to controls. METHODS: Between 1998 and 2008, 88 patients with radiological chondrocalcinosis (R-CCK) and 67 patients with histological chondrocalcinosis (H-CCK) were treated for end-stage medial compartment arthritis with Oxford UKA. One-to-two matching was performed to controls, treated with UKA, but without evidence of chondrocalcinosis. Functional outcome and implant survival were assessed in each group. RESULTS: The mean follow-up was 10 years. The mean Oxford Knee Score (OKS) at final follow-up was 43, 41 and 41 in H-CCK, R-CCK and control groups (change from baseline OKS was 21, 18 and 15, respectively). The change was significantly higher in H-CCK than in control but was not significantly different in R-CCK. Ten-year survival was 96 % in R-CCK, 86 % in H-CCK and 98 % in controls. Although the survival in H-CCK was significantly worse than in control, only one failure was due to disease progression. CONCLUSION: The presence of R-CCK does not influence functional outcome or survival following UKA. Pre-operative radiological evidence of CCK should not be considered to be a contraindication to UKA. H-CCK is associated with significantly improved clinical outcomes but also a higher revision rate compared with controls. LEVEL OF EVIDENCE: Case control study, Level III.

Trans-patella tendon approach for domed lateral unicompartmental knee arthroplasty does not increase the risk of patella tendon shortening.

PURPOSE: Shortening of the patella tendon has been noted after total knee arthroplasty and has been associated with diminished functional outcomes. Traumatic and/or ischaemic injury peri-operatively are suggested causes. The Oxford domed lateral unicompartmental knee arthroplasty (UKA) requires a vertical incision through the patella tendon to facilitate orientation of the proximal tibial saw cut; this may induce scarring or impair vascularity of the tendon and can cause shortening. This study investigated the hypothesis that the trans-patella tendon incision increases the incidence of patella tendon shortening after domed lateral UKA when compared to flat lateral UKA performed without the trans-patella tendon incision. METHODS: The radiographs of 50 patients who underwent domed lateral UKA, using the trans-patella tendon approach, and a cohort of 30 patients who underwent flat lateral UKA, in which an incision through the patella tendon was not employed, were reviewed retrospectively. The patella tendon length (PTL) and the Insall-Salvati ratio were measured. In addition, pre-operative and post-operative clinical scores were recorded using both the OKS and AKSS. A change in PTL of greater than or equal to 10 % was considered to be significant. RESULTS: In the domed lateral UKA group, 13 patients demonstrated a >10 % change in the PTL at 1-year post-surgery (2 shortened and 11 lengthened). In the flat lateral UKA group, nine patients demonstrated a significant change in the PTL at 1-year post-surgery (2 shortened and 7 lengthened). CONCLUSION: This study demonstrated that using a trans-patella approach during lateral domed UKA surgery did not significantly increase patella tendon shortening and did not result in reduced clinical outcomes.

Preoperative pain location is a poor predictor of outcome after Oxford unicompartmental knee arthroplasty at 1 and 5 years.

PURPOSE: Indications for unicompartmental knee arthroplasty (UKA) vary between units. Some authors have suggested, and many surgeons believe, that medial UKA should only be performed in patients who localise their pain to the medial joint line. This is despite research showing a poor correlation between patient-reported location of pain and radiological or operative findings in osteoarthritis. The aim of this study is to determine the effect of patient-reported preoperative pain location and functional outcome of UKA at 1 and 5 years. METHODS: Preoperative pain location data were collected for 406 knees (380 patients) undergoing Oxford medial UKA. Oxford Knee Score, American Knee Society Scores and Tegner activity scale were recorded preoperatively and at follow-up; 272/406 (67 %) had pure medial pain, 25/406 (6 %) had pure anterior knee pain, and 109/406 (27 %) had mixed or generalised pain. None had pure lateral pain. The primary outcome interval is 1 year; 132/406 patients had attained 5 years by the time of analysis, and their 5-year data are presented. RESULTS: At 1 and 5 years, each group had improved significantly by each measure [mean ΔOKS 15.6 (SD 8.9) at year 1, 16.3 (9.3) at year 5]. There was no difference between the groups, nor between patients with and without anterior knee pain or isolated medial pain. CONCLUSIONS: No correlation is demonstrated between preoperative pain location and outcome. We conclude that localised medial pain should not be a prerequisite to UKA and that it may be performed in patients with generalised or anterior knee pain.

The management of mobile bearing dislocation in the Oxford lateral unicompartmental knee replacement.

This article describes a technique to manage dislocations of mobile bearing lateral unicompartmental knee replacements. When dislocations occur, the bearing usually subluxes medially over the medial wall of the tibial component into the intercondylar notch. By positioning small fragment screws with their heads above the vertical wall, thereby increasing the height of the wall, subsequent dislocations can be prevented. Seven cases treated in this manner are reported, of which one of the seven has redislocated. In the remaining six, their clinical outcomes are comparable to the outcomes of those without dislocations.

Load transfer in the proximal tibia following implantation with a unicompartmental knee replacement: a static snapshot.

Unicompartmental knee replacement (UKR) is an appealing alternative to total knee replacement when the patient has isolated medial compartment osteoarthritis. A common observation post-operatively is radiolucency between the tibial tray wall and the bone. In addition, some patients complain of persistent pain over the proximal tibia antero-medially; this may be related to elevated bone strains in the tibia. Currently, there is no intentionally made mechanical bond between the vertical wall of an Oxford UKR and the adjacent bone; whether one exists or not will influence the load transmission in the proximal tibia and may affect the elevated tibia strain. The aim of this study was to investigate how introducing a mechanical tie between the tibial tray wall and the adjacent bone might alter the load carried into the tibia for both cemented and cementless UKRs. Strain energy density in the region of bone adjacent to the tray wall was considerably increased when a mechanical tie was introduced; this has the potential of reducing the likelihood of a radiolucency occurring in that region. Moreover, a mechanical tie had the effect of reducing proximal tibia strain, which may decrease the incidence of pain following implantation with a UKR.

Five-year results of a randomised controlled trial comparing cemented and cementless Oxford unicompartmental knee replacement using radiostereometric analysis.

BACKGROUND: Cementless fixation is an alternative to cemented unicompartmental knee replacement (UKR). The aim of this study was to determine if cementless UKR fixation is as good as cemented by comparing the five-year migration measured radiostereometric analysis (RSA) in a randomised controlled trial. METHODS: Thirty-nine patients were randomised to receive either a cemented or a cementless Oxford UKR and were studied at intervals up to five years to assess migration with RSA and radiolucencies with radiographs. RESULTS: During the first year there was a small and significant amount of migration, predominantly in an anterior direction, of both the cemented (0.24 mm, SD 0.32, p = 0.01) and cementless (0.26 mm, SD 0.31, p = 0.00) femoral components. Thereafter there was no significant migration in any direction. At no stage was there any significant difference between the migrations of the cemented or cementless femoral components. During the first year, particularly the first three months, the cementless tibial components subsided 0.28 mm (SD 0.19, p = 0.00). This was significantly (p = 0.00) greater than the subsidence of the cemented tibial component (0.09, SD 0.19, p = 0.28). Between the second and fifth years there was no significant migration of either cemented or cementless tibial components. At five years radiolucent lines occurred significantly less with cementless (one partial) compared to cemented (six partial and one complete) tibial components. CONCLUSIONS: As, between two and five years, there was no significant migration of cemented or cementless components, and no significant difference between them, we conclude that cementless fixation is as reliable as cemented. It may be better as there are fewer radiolucent lines.

Age stratified, matched comparison of unicompartmental and total knee replacement.

BACKGROUND: Unicompartmental knee replacement (UKR) tends to provide better function but has a higher revision rate than total knee replacement (TKR). The aim was to determine if this occurred in all age groups. METHODS: Two large, non-registry, prospective cohorts with median 10-year follow-up (2252 TKR, 1000 medial UKR) were identified. All UKR met recommended indications. TKR with an inappropriate disease pattern for medial UKR were excluded. Knees were propensity score-matched within age-strata (<60 years at operation, 60 to <75, 75+) and compared using Oxford Knee Score (OKS), Kaplan-Meier revision rates and a composite failure, defined as any of revision, reoperation or no improvement in OKS. RESULTS: One thousand five hundred and eighty-two TKR and UKR were matched. Results are reported TKR vs UKR for ages <60, 60 to <75 and 75+. Median 10-year OKS were 33 vs 45 (p < 0.001), 36 vs 42 (p < 0.001) and 36 vs 38 (p = 0.25). Ten-year revision rates were 11% vs 7%, 5% vs 5%, and 5% vs 10%, (none significant). The composite failures occurred 8%, 5% and 5% more frequently with TKR than UKR (none significant). CONCLUSIONS: In this matched study UKR provided better functional outcomes in all age groups, particularly the young, and provided substantially more excellent outcomes. Although in older groups TKR tended to have a lower revision rate, in the young UKR had a lower revision rate. This was surprising and was perhaps because in this study UKR was, as recommended, only used for bone-on-bone arthritis, whereas in young patients it is widely used for early arthritis, which is associated with a high failure rate. This study supports the use of UKR with recommended indications, in all age groups.

Mid- to long-term function and implant survival of ACL reconstruction and medial Oxford UKR.

PURPOSE: The purpose of this study was to describe mid- to long-term outcomes of anterior cruciate ligament (ACL) reconstruction with simultaneous or staged medial unicompartmental knee replacement (UKR), and compare outcomes between (1) young patients aged younger than 55 at surgery and those older, (2) those with long-term follow-up greater than 10 years, (3) cemented and cementless UKR, and (4) compare outcomes to those with an intact ACL. PATIENTS AND METHODS: We identified knees with staged or simultaneous ACL reconstruction and medial UKR from a prospectively followed designer UKR cohort, and describe mean Oxford Knee Score (OKS), mean Tegner activity score and Kaplan-Meier survival estimates. We matched these knees to ACL-intact knees. RESULTS: Seventy-six consecutive UKR with staged or simultaneous ACL reconstruction were identified with mean six-year follow-up (range 1-15). There was significant improvement in OKS and Tegner score with surgery. At most recent follow-up, OKS was 41.0 (range 11 to 48), and Tegner score 3.6 (0 to 8). There were three revisions occurring at a mean of five years post-operatively. The five-, 10- and 15-year survival estimates were 97% (95% confidence interval [CI] 93-100), 92% (83-100), and 92% (83-100). There was no difference in functional scores or implant survival in young patients, those with long-term follow-up (>10 years), those with cementless fixation, or when compared to ACL intact knees. CONCLUSION: These results demonstrate excellent mid- to long-term function and survival of selected patients who have undergone ACL reconstruction and medial UKR. Their outcome was similar to those with intact ACLs.

Functional Outcome and Revision Rate Are Independent of Limb Alignment Following Oxford Medial Unicompartmental Knee Replacement.

BACKGROUND: There is controversy about optimal limb alignment following knee replacement. An aim of using Oxford medial unicompartmental knee replacement (UKR) implants is to accurately restore normal ligament tension in the knee, thereby restoring normal kinematics. This return to normal tension typically results in a return to prearthritic alignment, which is frequently varus. The aim of this study was to investigate the relationship between postoperative limb alignment and postoperative patient-reported outcome and implant revision rate. METHODS: We used a consecutive cohort of 891 knees with cemented Oxford medial UKR implants with a mean 10-year follow-up and recorded alignment. We grouped knees according to postoperative mechanical alignment as marked varus (estimated at 10°), mild varus (estimated at 5°), neutral, and valgus. The mean Oxford Knee Score (OKS) was calculated at 5 and 10 years postoperatively. Revision risk was assessed by survival analysis and component-time incidence rates. RESULTS: Postoperatively, 67 (8%) of the 891 knees were in marked varus; 308 (35%), in mild varus; 508 (57%), in neutral; and 8 (1%), in valgus. The valgus group (8 knees) was too small for further analysis. The mean OKS (and standard deviation [SD]) at 10 years postoperatively was 41.7 ± 7 for marked varus, 40.5 ± 8 for mild varus, and 39.4 ± 9 for neutral alignment (p = 0.28). At 10 years, 92%, 85%, and 76% achieved a good or excellent OKS outcome, respectively (p = 0.02). Twelve-year survival rates were 93.3% for marked varus, 93.2% for mild varus, and 93.6% for neutral alignment, respectively (p = 0.53). Revision incidence rates per 100 component-years were 0.49 (95% confidence interval [CI], 0.2 to 1.5), 0.36 (95% CI, 0.2 to 0.7), and 0.54 (95% CI, 0.4 to 0.8), respectively, and were not significantly different (p = 0.53). CONCLUSIONS: Marked postoperative varus mechanical alignment of an estimated 10° was present in 8%, and mild varus of about 5° was present in 35%. Increasing varus alignment was associated with an increasing percentage of good or excellent OKS outcomes, but otherwise there were no significant differences between alignment groups in patient-reported outcome or revision rate. These data support the standard operative technique for the Oxford UKR, which aims to restore ligament tension and therefore prearthritic alignment rather than neutral mechanical alignment. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The Oxford unicompartmental knee arthroplasty: a radiological perspective.

Unicompartmental knee arthroplasty (UKA) is increasingly being performed in both specialist centres as well as district hospitals. The radiologists should be aware of the required preoperative imaging, the normal appearance, and complications of this procedure. Unfortunately, very little is available in the radiology literature. This review aims to provide a radiological perspective to an already widely used procedure.

Combined anterior cruciate reconstruction and Oxford unicompartmental knee arthroplasty: in vivo kinematics.

The in vivo kinematics of 10 patients after combined anterior cruciate ligament reconstruction (ACLR group) and Oxford unicompartmental knee arthroplasty (UKA) was compared to those of 10 Oxford UKA patients with an intact ACL (ACLI group) and a group of 22 normal knees. The kinematics during a step-up exercise and a deep knee bend exercise was measured using a fluoroscopic technique. The patellar tendon angle (PTA) to knee flexion angle relationship during both exercises was similar for all three groups of subjects. For the UKA groups the pattern of mobile bearing movement during both exercises was similar. This study demonstrates that normal knee kinematics is achieved in the ACL deficient arthritic knee following ACLR and UKA. As a result these patients, who tend to be young and high demand, have excellent outcome and achieve high levels of function. As the relative position of the components and thus component loading are similar to the ACLI UKA, we would expect similar long term survival.

Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement.

OBJECTIVES: The primary stability of the cementless Oxford Unicompartmental Knee Replacement (OUKR) relies on interference fit (or press fit). Insufficient interference may cause implant loosening, whilst excessive interference could cause bone damage and fracture.The aim of this study was to identify the optimal interference fit by measuring the force required to seat the tibial component of the cementless OUKR (push-in force) and the force required to remove the component (pull-out force). MATERIALS AND METHODS: Six cementless OUKR tibial components were implanted in 12 new slots prepared on blocks of solid polyurethane foam (20 pounds per cubic foot (PCF), Sawbones, Malmo, Sweden) with a range of interference of 0.1 mm to 1.9 mm using a Dartec materials testing machine HC10 (Zwick Ltd, Herefordshire, United Kingdom) . The experiment was repeated with cellular polyurethane foam (15 PCF), which is a more porous analogue for trabecular bone. RESULTS: The push-in force progressively increased with increasing interference. The pull-out force was related in a non-linear fashion to interference, decreasing with higher interference. Compared with the current nominal interference, a lower interference would reduce the push-in forces by up to 45% (p < 0.001 One way ANOVA) ensuring comparable (or improved) pull-out forces (p > 0.05 Bonferroni post hoc test). With the more porous bone analogue, although the forces were lower, the relationship between interference and push-in and pull-out force were similar. CONCLUSIONS: This study suggests that decreasing the interference fit of the tibial component of the cementless OUKR reduces the push-in force and can increase the pull-out force. An optimal interference fit may both improve primary fixation and decrease the risk of fracture.Cite this article: S. Campi, S. J. Mellon, D. Ridley, B. Foulke, C. A. F. Dodd, H. G. Pandit, D. W. Murray. Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement. Bone Joint Res 2018;7:226-231. DOI: 10.1302/2046-3758.73.BJR-2017-0193.R1.

Ten-year survival and seven-year functional results of cementless Oxford unicompartmental knee replacement: A prospective consecutive series of our first 1000 cases.

BACKGROUND: Cementless fixation is an alternative to cemented unicompartmental knee replacement (UKR), with several advantages over cementation. This study reports the ten-year survival and seven-year clinical outcome of cementless Oxford unicompartmental knee replacement (OUKR). METHODS: This prospective study describes the clinical outcome and survival of the first 1000 consecutive cementless medial OUKRs implanted at two centres for recommended indications. RESULTS: The 10-year survival was 97% (CI 95%: 92-100%), with 25 knees being revised. The commonest reason for revision was progression of arthritis laterally, which occurred in nine knees, followed by primary dislocation of the bearing, which occurred in six knees. There were two dislocations secondary to trauma and a ruptured ACL, and two tibial plateau fractures. Although there were no definite cases of aseptic loosening, two early revisions were related to tibial fixation: one for pain and a radiolucent line and one for incomplete seating of the component with a radiolucent line. There were four revisions for pain, but the cause of the pain was uncertain: in one there was tibial overhang and in two there was patellofemoral degeneration, which possibly contributed to the pain. There were no deep infections. The mean OKS improved from 23 (SD 8) to 42 (SD 7) at a mean follow-up of 7.0 years (p < 0.001). There was no significant difference in survival or clinical outcome between the designer and independent centre. CONCLUSIONS: The cementless OUKR is a safe and reproducible procedure with excellent 10-year survival and clinical results in the hands of both designer and independent surgeons.

The influence of the presence and severity of pre-existing patellofemoral degenerative changes on the outcome of the Oxford medial unicompartmental knee replacement.

Patellofemoral joint degeneration is often considered a contraindication to medial unicompartmental knee replacement. We examined the validity of this preconception using information gathered prospectively on the intra-operative status of the patellofemoral joint in 824 knees in 793 consecutive patients who underwent Oxford unicondylar knee replacement for anteromedial osteoarthritis. All operations were performed between January 1998 and September 2005. A five-point grading system classified degeneration of the patellofemoral joint from none to full-thickness cartilage loss. A subclassification of the presence or absence of any full-thickness cartilage loss was subsequently performed to test selected hypotheses. Outcome was evaluated independently by physiotherapists using the Oxford and the American Knee Society Scores with a minimum follow-up of one year. Full-thickness cartilage loss on the trochlear surface was observed in 100 of 785 knees (13%), on the medial facet of the patella in 69 of 782 knees (9%) and on the lateral facet in 29 of 784 knees (4%). Full-thickness cartilage loss at any location was seen in 128 knees (16%) and did not produce a significantly worse outcome than those with a normal or near-normal joint surface. The severity of the degeneration at any of the intra-articular locations also had no influence on outcome. We concluded that, provided there is not bone loss and grooving of the lateral facet, damage to the articular cartilage of the patellofemoral joint to the extent of full-thickness cartilage loss is not a contraindication to the Oxford mobile-bearing unicompartmental knee replacement.

Pre-operative clinical and radiological assessment of the patellofemoral joint in unicompartmental knee replacement and its influence on outcome.

Anterior knee pain and/or radiological evidence of degeneration of the patellofemoral joint are considered to be contraindications to unicompartmental knee replacement. The aim of this study was to determine whether this is the case. Between January 2000 and September 2003, in 100 knees (91 patients) in which Oxford unicompartmental knee replacements were undertaken for anteromedial osteoarthritis, pre-operative anterior knee pain and the radiological status of the patellofemoral joint were defined using the Altman and Ahlback systems. Outcome was evaluated at two years with the Oxford knee score and the American Knee Society score. Pre-operatively 54 knees (54%) had anterior knee pain. The clinical outcome was independent of the presence or absence of pre-operative anterior knee pain. Degenerative changes of the patellofemoral joint were seen in 54 patients (54%) on the skyline radiographs, including ten knees (10%) with joint space obliteration. Patients with medial patellofemoral degeneration had a similar outcome to those without. For some outcome measures patients with lateral patellofemoral degeneration had a worse score than those without, but these patients still had a good outcome, with a mean Oxford knee score of 37.6 (SD 9.5). These results show that neither anterior knee pain nor radiologically-demonstrated medial patellofemoral joint degeneration should be considered a contraindication to Oxford unicompartmental knee replacement. With lateral patellofemoral degeneration the situation is less well defined and caution should be observed.

Introduction of a new mobile-bearing total knee prosthesis: minimum three year follow-up of an RCT comparing it with a fixed-bearing device.

As part of the step-wise validation of a new prosthesis (TMK), we previously published the 1 year results of a randomised controlled trial in patients undergoing bilateral knee replacement [Price A., Rees J., Beard D., Juszczak E. et al. A mobile-bearing total knee prosthesis compared with a fixed-bearing prosthesis. JBJS B 2003;85-B-1:62-7.]. Forty patients had the new mobile-bearing prosthesis implanted in one knee and an established fixed-bearing device in the other (AGC). We now report the 3 year status of these patients and, in addition, review a separate multi-centre cohort of 172 patients who had undergone unilateral arthroplasty with the TMK. No significant differences were found in outcome (American Knee Society Score and Oxford Knee Score) between the two prostheses. The greater incidence of "clicking" in the mobile-bearing knee, reported in the previous review, persisted (TMK=48%, AGC=30%). The presence of this mechanical noise was found to have no relationship with outcome in either of the prostheses. The unilateral cohort study showed an acceptable complication rate for the new prosthesis, although some patients reported subjective instability. The method of controlled introduction of the TMK, of which this constitutes a further step, has allowed us to assess the significance of a reported problem (clicking) and to provide scientific data from which other surgeons can decide about use of the implant.