Lateral Unicompartmental Knee Replacement Research Articles

Mechanisms of mobile bearing dislocation in lateral unicompartmental knee replacement.

Mobile bearing dislocation occurs in 1- 6% of Oxford Domed Lateral replacements. Dislocations are predominantly medial, but can occur anteriorly or posteriorly. They tend to occur when the knee is flexed. It is not clear how dislocations can be prevented. A previously described mechanical rig for assessing mobile bearing dislocation was updated so as to study dislocation with the knee in flexion. Sub-categories for the description of each type of dislocation were introduced. Dislocation was only possible when the knee was distracted. As the amount of distraction possible in the knee is variable, the risk of dislocation is related to the amount of distraction in the rig necessary for a dislocation. The type of dislocation requiring the least distraction was medial `edge' dislocation in which the edge of the bearing dislocates onto the tibial wall, which is the most common type of dislocation. The amount of distraction necessary decreased the further the bearing was from the wall and with 50% posterior overhang. Rotation of the knee did not influence the amount of distraction. In conclusion dislocation can only occur if the lateral compartment is distracted. To reduce the dislocation risk, surgeons should aim to position the femoral and tibial components so that the bearing is as close as possible to the wall without jamming against it and the tibial component should be positioned flush with the posterior tibial cortex. If, during the surgery, the mobile bearing can easily be dislocated onto the wall the surgeon should consider changing to a fixed bearing. The tibial component should also be positioned flush with the posterior tibial cortex, as if it is too far forward this may contribute to dislocation.

Fixed lateral unicompartmental knee replacement is a reliable treatment for lateral compartment osteoarthritis after mobile-bearing medial unicompartmental replacement

PurposeLateral osteoarthritis following medial unicompartmental knee replacement (UKR) is usually treated with total knee replacement, however, lateral UKR is a less invasive option that preserves a well-functioning medial UKR. This study aimed to determine the 5-year outcome of the cemented Fixed Lateral Oxford UKR (FLO) when used for the treatment of severe lateral disease after medial Oxford unicompartmental knee replacement.MethodsForty-four knees with lateral bone-on-bone osteoarthritis (n = 43) and avascular necrosis (n = 1) treated with the FLO following medial Oxford UKR were followed up prospectively. The Oxford Knee Score (OKS) and Tegner Activity Score (TAS) were collected pre- and post-operatively. Life-table analysis was used to determine survival rates.ResultsThe mean patient age at the time of FLO surgery was 74.4 years with a mean time of 12.1 years between the primary medial UKR and the conversion to a bi-UKR with a FLO. Mean follow-up of the FLO was 3.5 years. After FLO no intra-operative or medical complications, re-admissions, or mortality occurred. There was one reoperation in which a bearing was exchanged for a medial bearing dislocation. There were no revisions of the FLO, so the FLO survival rate at 5 years was 100% (24 at risk). The mean pre-operative OKS was 22, which significantly (p < 0.0001) improved to a mean of 42, 42, and 40 at 1, 2, and 5 years, respectively. The median TAS had a non-significant improvement from 2.5 (Range 0–8) pre-operatively to 2 (Range 1–6) at 5 years postoperatively.ConclusionThe FLO is a reliable treatment for lateral osteoarthritis following medial UKR. At 5 years there was a 100% survival of the FLO with a mean OKS of 40.Level of evidenceIV, Prospective Case Series.

Fixed-bearing is superior to mobile-bearing in lateral unicompartmental knee replacement: a retrospective matched-pairs analysis

PurposeDue to low incidence of isolated lateral osteoarthritis (OA), there are limited data on whether a fixed-bearing (FB) or a mobile-bearing (MB) design is superior for lateral unicompartmental knee replacement (UKR). The aim of this matched-pairs analysis was to compare both designs in terms of implant survival and clinical outcome.MethodsPatients who received MB-UKR (Group A) and FB-UKR (Group B) at a single centre were matched according to gender, age at time of surgery and body mass index (BMI). Survivorship analysis was performed with the endpoint set as “revision for any reason”. Clinical outcome was assessed using the Oxford knee score (OKS), visual analogue scale for pain (VAS), patients’ satisfaction, University of California Los Angeles activity scale (UCLA) and the Tegner activity score (TAS).ResultsA total of 60 matched pairs were included with a mean follow-up (FU) of 3.4 ± 1.3 (range 1.2–5.0) years in Group A and 2.7 ± 1.2 (range 1.0–5.0) years in Group B. Survivorship between both groups differed significantly (Group A: 78.7%; Group B: 98.3%, p = 0.003) with bearing dislocation being the most common reason for revision in Group A (46.2%). The relative and absolute risk reduction were 92.2% and 20%, respectively, with 5 being the number needed to treat. There were no differences in OKS (Group A: 41.6 ± 6.5; Group B: 40.4 ± 7.7), VAS (Group A: 2.9 ± 3.2; Group B: 1.6 ± 2.2), UCLA (Group A: 5.7 ± 1.3; Group B: 5.9 ± 1.8) and TAS (Group A: 3.0 ± 1.0; Group B: 3.1 ± 1.2) between both groups on follow-up.ConclusionDespite modern prosthesis design and surgical technique, implant survival of lateral MB-UKR is lower than that of FB-UKR on the short- to mid-term due to bearing dislocation as the most common cause of failure. Since clinical results are equivalent in both groups, FB-UKR should be preferred in treatment of isolated lateral OA.Level of evidenceRetrospective case–control study, Level III.

Short- to mid-term results of minimally invasive lateral unicompartmental knee replacement: 133 cases in a non-designer series

IntroductionThe aim of the current study was to demonstrate short- to mid-term survivorship as well as clinical outcome of lateral unicompartmental knee replacement (UKR) with a fixed-bearing (FB) design from a non-designer center using the Oxford Fixed Lateral prosthesis.Materials and methodsThis single-center retrospective cohort study reports the results of 133 consecutive lateral FB-UKR. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford-Knee-Score (OKS), American-Knee-Society-Score (AKSS-O), range-of-motion (ROM) and visual-analog-scale for pain (VAS).ResultsThere were two revision surgeries with conversion to total knee replacements (TKR) due to persistent pain resulting in a survival rate of 98.5% (95% CI 93.5–99.6) with a mean follow-up (FU) of 3.3 ± 1.8 years (range 1–8.5). All outcome scores, VAS and ROM showed a significant improvement at final FU (p < 0.001). The OKS improved from 26 ± 7.8 (range 11–45) preoperatively to 39 ± 8.3 (range 13–48), the AKSS-O from 49.2 ± 14.6 (range 18–90) to 81.8 ± 15.1 (range 40–100), the AKSS-F from 53 ± 23.7 (range 0–100) to 80.4 ± 21.4 (range 5–100) and the ROM from 118 ± 17 (range 90–160) to 134 ± 9.5 (range 100–155).ConclusionsThe short- to mid-term results following lateral FB-UKR demonstrate a high survivorship and good clinical outcome from an independent series. We, therefore, suggest that FB-UKR is a safe treatment option for isolated lateral OA if sufficient surgical experience is provided.Level of evidenceRetrospective cohort study, level IV.

TEN YEARS OF COMBINED ACL RECONSTRUCTION AND UNICOMPARTMENTAL KNEE ARTHROPLASTIES

The purpose of this study is to assess the long term results of combined ACL reconstruction and unicompartmental knee replacements (UKR). These patients have been selected for this combined operation due to their combination of instability symptoms from an absent ACL and unicompartmental arthritis.Retrospective review of 44 combined UKR and ACL reconstruction by a single surgeon. Surgeries included both medial and lateral UKR combined with either revision ACL reconstruction or primary ACL reconstruction. Patient reported outcomes were obtained preoperatively, at one year, 5 years and 10 years. Revision rate was followed up over 13 years for a mean of 7.4 years post-surgery.The average Oxford score at one year was 43 with an average increase from pre-operation to 1 year post operation of 15. For the 7 patients with 10 year follow up average oxford score was 42 at 1 year, 43 at 5 years and 45 at 10 years.There were 5 reoperations. 2 for revision to total knee arthroplasty and 1 for an exchange of bearing due to wear. The other 2 were the addition of another UKR. For those requiring reoperation the average time was 8 years.Younger more active patients presenting with ACL deficiency causing instability and unicompartmental arthritis are a difficult group to manage. Combining UKR and ACL reconstruction has scant evidence in regard to long term follow up but is a viable option for this select group. This paper has one of the largest cohorts with a reasonable follow up averaging 7.4 years and a revision rate of 11 percent.Combined unilateral knee replacements and ACL reconstruction can be a successful operation for patients with ACL rupture causing instability and unicompartmental arthritis.

Physical Activity of Young Patients following Minimally Invasive Lateral Unicompartmental Knee Replacement.

Unicompartmental knee replacement (UKR) has increased in popularity in recent years, especially in young patients with high demands on their athletic ability. To date, there are no data available on the physical activity of young patients following lateral UKR. The aim of this study was to demonstrate return-to-activity rate and sporting activity of patients aged 60 years or younger following lateral UKR with a fixed-bearing (FB) prosthesis. Thirty-seven patients aged 60 years or younger after lateral FB-UKR were included. Sporting activities were assessed using the University of California Los Angeles activity scale (UCLA) and the Tegner activity score (TAS). Clinical outcome was measured using the Oxford Knee Score (OKS), range of motion (ROM) and visual analogue scale (VAS). The mean follow-up (FU) was 3.1 ± 1.5 years and the mean age at surgery was 52.8 ± 3.1 years. The return-to-activity rate was 87.5% and 49% of patients were highly active postoperatively as defined by an UCLA score of 7 or higher. All clinical parameters increased significantly postoperatively. We demonstrated a high return-to-activity rate with nearly half of the patients achieving high activity levels. Longer FU periods are necessary to evaluate the effect of activity on implant survival.

Early results of fixed-bearing unicompartmental knee replacement designed for the lateral compartment

BackgroundIsolated lateral compartment knee arthritis is less prevalent than medial. While the reported results of medial unicompartmental knee replacement (UKR) have been good and comparable to total knee replacement, the results of lateral UKR have been mixed. We present the short-term results and survivorship of a fixed-bearing UKR designed specifically for the lateral compartment.MethodsWe report the result of 130 primary fixed-bearing lateral Oxford (FLO) UKRs (123 patients) performed between 2015 and 2019 with a minimum follow-up of 1 year. The indications for lateral UKR were: isolated lateral osteoarthritis (n = 122), post-trauma (n = 5) and osteonecrosis (n = 3). The mean age was 69.1 (± 11.6), mean BMI 28.4 (± 4.9), 66.9% female, 60% right-sided, and mean follow-up 3 (range 1–4.8 years, standard deviation ± 1) years. The primary outcome measure was the Oxford knee score (OKS). Survival analysis was performed with “revision for any reason”, “reoperation”, and “implant failure” as the endpoints.ResultsSix patients died from unrelated reasons. None of the implants failed. One required the addition of a medial UKR for medial arthritis. There were no other reoperations. At 4 years, the survival for implant failure was 100% and for both revision and all reoperations was 99.5% (95% CI 96.7–99.9%). At the last review, at a mean of 3 years, the mean Oxford knee score was 41.ConclusionThe good survivorship and outcome scores suggest that UKR designed for the lateral compartment is an excellent alternative to total knee replacement in selected patients with isolated lateral tibiofemoral arthritis at short-term follow-up.

Cemented Lateral Unicompartmental Knee Replacement: A retrospective single centre independent series

Background Unicompartmental knee replacement (UKR) has functional and economic benefits when compared with total knee replacement, however it is technically demanding and may be associated with higher failure rates. The primary aim of this independent series study was to evaluate the survival of lateral UKRs implanted in our institution and their clinical outcomes. The secondary outcome was to compare the results of mobile and fixed-bearing prostheses. Methods This is a retrospective series study of 183 cemented lateral UKRs implanted in 170 patients, for advanced isolated lateral compartment arthritis, under the care of two senior surgeons. Fixed or mobile-bearing prostheses were used according to the surgeon's preference. Kaplan Meier analysis was used to evaluate prosthesis survival with the endpoint being revision for any reason. A subgroup analysis of survival was also done for each bearing type. Functional outcomes were evaluated using the Oxford knee score (OKS) at final follow-up. Results This series included 103 Fixed-bearing and 80 mobile-bearing prostheses. Median follow-up was 6.9 years. 9 knees required revision. The commonest reason for revision was progression of arthritis to the medial compartment. Dislocation was the commonest cause of revision in the mobile-bearing group. Survival at 10 years was 91.9% with no significant difference ( p = 0.083) between bearing types (fixed-bearing 93.8% and mobile-bearing 90.6%). The OKS were comparable in both groups, the mean OKS was 44/48. Conclusion Good survival and functional outcomes can be achieved using cemented lateral UKRs with both bearing types. There was a trend towards superior outcomes in the fixed-bearing group.

Application of a robotics path planning algorithm to assess the risk of mobile bearing dislocation in lateral unicompartmental knee replacement

Due to ligament laxity, bearing dislocation occurs in 1–6% of Oxford Domed Lateral (ODL) replacements with most dislocations occurring medially. Dislocations were studied using a previously built mechanical rig, however testing using the rig was inefficient. The aim of this study was to develop a better tool that was more reliable and efficient. An established robotics software package, the Open Motion Planning Library, was modified to accept the ODL components. Using a robotics path planning algorithm, the mobile bearing was allowed to find a way out from between the femoral and tibial components i.e. to dislocate. Testing assessed a range of clinically relevant positions of the femoral component relative to the tibial component. Dislocations were labelled as medial, lateral, anterior or posterior depending on the dislocation direction. The Distraction to Dislocation (DD) measured the minimum vertical distraction of the femoral component from the tibial component for a dislocation to occur. Results were validated against the mechanical rig. Statistical analysis of medial dislocation showed excellent agreement with an intraclass correlation value of 0.993 (95% CI 0.982–0.998). All DDs from the dislocation analysis tool were within 1 mm of the mechanical rig DDs with results sharing a remarkably similar trend. The robotics dislocation analysis tool output DDs which were marginally higher than the manual mechanical rig: 0.50 mm anteriorly, 0.25 mm posteriorly and 0.50 mm laterally. Medially, the computational DD differed on average by 0.09 mm (stand deviation: 0.2026 mm). Our study describes the development and validation of a novel robotics dislocation analysis tool, which allows mobile bearing dislocation risk quantification. The tool may also be used to improve surgical implantation parameters and to assess new implant designs that aim to reduce the medial dislocation risk to an acceptable level.

The Oxford Domed Lateral Unicompartmental Knee Replacement implant: Increasing wall height reduces the risk of bearing dislocation.

Due to lateral ligament laxity, bearing dislocation occurs in 1%–6% of Oxford Domed Lateral replacements. Most dislocations are medial but they do rarely occur anteriorly or posteriorly. The aim was to decrease the risk of dislocation. For a bearing to dislocate the femoral component has to be distracted from the tibial component. A robotic-path-planning-algorithm was used with a computer model of the implant in different configurations to determine the Vertical Distraction needed for Dislocation (VDD). With current components, VDD anteriorly/posteriorly was 5.5 to 6.5 mm and medially was 3.5 to 5.75 mm. A thicker bearing increased VDD medially and decreased VDD anteriorly/posteriorly (0.1 mm/1 mm thickness increase). VDD medially increased with the bearing closer to the tibial wall (0.5 mm/1 mm closer), or by increasing the tibial wall height (1 mm/1 mm height increase). VDD anteriorly/posteriorly was not influenced by bearing position or wall height. To prevent collision between the femoral and tibial components an increase in wall height must be accompanied by a similar increase in minimum bearing thickness. Increasing the wall height and minimum bearing thickness by 2 mm and ensuring the bearing is 4 mm or less from the wall increased the minimum VDD medially to 5.5 mm. The lower VDD medially than anteriorly/posteriorly explains why medial dislocation is more common. If the wall height is increased by 2 mm, the minimum bearing thickness is 5 mm and the surgeon ensured the bearing is 4 mm or less from the wall, the medial dislocation rate should be similar to the anterior/posterior dislocation rate, which should be acceptable.

Oxford Lateral Uni-Compartmental Knee Replacement: Up-to 10 years Follow-up from an Independent Series

Oxford Lateral Uni-Compartmental Knee Replacement: Up-to 10 years Follow-up from an Independent Series

Minimally invasive lateral unicompartmental knee replacement: Early results from an independent center using the Oxford fixed lateral prosthesis

PurposeThe aim of the present study was to assess clinical outcome as well as short-term survivorship of fixed-bearing lateral unicompartmental knee replacement (UKR) from a non-designer centre using the Oxford Fixed Lateral prosthesis. MethodsThis single-centre retrospective cohort study reports the short-term results of 51 consecutive patients (52 knees) after fixed-bearing lateral UKR with a minimum follow-up of one year. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford Knee Score (OKS), objective American Knee Society Score (AKSS-O), range-of-motion (ROM), visual analog scale for pain (VAS), Tegner activity score and UCLA score. ResultsThere was no revision surgery, defined as exchange of at least one of the components resulting in a survival rate of 100% at two years. Three patients required further surgical treatment resulting in a survival rate of 94.2% (95% confidence interval (CI): 83.2–98.1%) with the endpoint ‘any reoperation’. Outcome scores, VAS and ROM showed a statistically significant improvement at final follow-up (P < .001). The OKS improved from 26.4 ± 6.9 (12–41) preoperatively to 39.7 ± 8.4 (15–48), the AKSS-O from 54.3 ± 15.3 (18–90) to 82.2 ± 15.6 (40–100), the American Knee Society Functional Score from 56.4 ± 21.3 (10–100) to 83.1 ± 20.2 (five to 100) and the ROM from 123.5 ± 13.5 (90–140) to 134 ± 10.3 (95–150). ConclusionEarly results of fixed-bearing lateral UKR using the Oxford-Fixed-Lateral prosthesis were encouraging with a significant improvement in pain and knee function as well as an excellent survivorship of 100% at a mean follow-up of two years. Further follow-up is necessary to evaluate the long-term effectiveness of this device and the surgical technique. Level of EvidenceLevel IV, retrospective cohort study.

Mid-term outcomes of mobile-bearing lateral unicompartmental knee arthroplasty

BackgroundThis research was undertaken to evaluate Oxford Domed Lateral unicompartmental knee replacement (UKR) survival and clinical and radiological outcomes. The study also considered the influence of body mass index (BMI) on results and proposed contralateral healthy knee anatomic femorotibial angle (AFTA) as a predictor of postoperative knee alignment. MethodsA retrospective evaluation of 41 primary Oxford Domed Lateral UKR performed in 41 patients in the same institution was undertaken on a patient group comprising of 10 men and 31 women with a mean age of 63 years (range: 38–81 years). A minimum follow-up of two years was required. ResultsThe total revision rate was one out of 41 patients (2.4%), with a mean follow-up of 49 months (range: 25–84 months). One patient presented with a traumatic medial dislocation of the bearing after 15 months (resulting in an overall dislocation rate of 2.4%). The visual analogue scale (VAS) and the Oxford knee score (OKS) demonstrated significant postoperative improvement (P < 0.001). Survival at five years, with revision for any reason as the endpoint, was 97.5%. No significant correlation was observed between BMI and postoperative flexion angle, radiologically measured parameters, or pre- and postoperative VAS and OKS. Significant correlation was found (r = 0.77, P < 0.001) between postoperative and contralateral healthy knee anatomic femorotibial angles. ConclusionsThe Oxford Domed Lateral UKR presents a low dislocation rate and excellent mid-term clinical and functional results. Contralateral healthy knee AFTA appears to be a predictor of postoperative knee alignment.

0056 - The Effect of Implant Position on Bone Strain Following Lateral Unicompartmental Knee Replacement: A Biomechanical Model using Digital Image Correlation

0056 - The Effect of Implant Position on Bone Strain Following Lateral Unicompartmental Knee Replacement: A Biomechanical Model using Digital Image Correlation

Lateral unicompartmental knee replacement: a systematic review of reasons for failure.

Currently, individual studies lack the power to successively illustrate different failure modes; therefore, we undertook a systematic review to examine lateral unicompartmental knee replacement (lat UKR) failure modes. Furthermore, we compared early with midterm and late failures and fixed-bearing with mobile-bearing implants. A search using the databases of PubMed, EMBASE, Cochrane, and annual registries was performed to search for failed lat UKRs. Studies were included when they reported more than four failures,described failure modesandwere minimum level IV studies. Data was analysed based on overall failure modes, fixed- vs. mobile bearing andearly (<5years) vs. midterm (5-10years) vs. late failures (>10years). Fourteen cohort studies and two registry-based studies were included. A total of 336 overall failures, 87 time-dependent failures, and 175 implant-specific failures were identified. The main overall causes of failure were osteoarthritis (OA) progression (30%) and aseptic loosening (22%). These were followed by less common causes such as instability (7%), unexplained pain (5%), infection (5%), polyethylene wear (5%), and bearing dislocation (5%). Bearing dislocation was the most common early failure (29%) and also the most common failure among mobile-bearing implants (27%). In midterm and late failures, OA progression had the highest rates (59% and 78% respectively) and was also the most common type of failure in fixed-bearing implants (44%). Progression of OA and aseptic loosening are the major overall failure modes in lat UKR. Bearing dislocation was the main failure mode in early years and in mobile-bearing implants, whereas OA progression caused most failures in late years and in fixed-bearing implants. Systematic Review of minimum level IV studies.

Patient-specific instrumentation improves alignment of lateral unicompartmental knee replacements by novice surgeons

PurposePatient-specific instrumentation (PSI) has the potential to offer numerous benefits—not least of all, improved resection accuracy; but its potential has not been realised in clinical studies. An explanation may be the focus of such studies on the total knee replacement (TKR—a common procedure, with which surgeons are generally very familiar. Consequently, we sought to investigate the potential role of PSI in guiding novice surgeons to perform the more technically demanding and less familiar lateral unicondylar knee replacement (LUKR).MethodsTwelve orthopaedic trainees naive to LUKR were instructed to perform the procedure according to a pre-operative plan. These were carried out on synthetic sawbones and were completed once with conventional instrumentation alone and once with the adjunct of PSI, allowing a comparison of the plan adherence achieved by the two sets of instrumentation.ResultsThere was a tendency for PSI to demonstrate improved plan adherence, though a statistically significant improvement was only seen in compound rotational error of the femoral implant (p = 0.004). PSI was, however, able to produce narrower standard deviations in the mean translational displacement of the femoral implant and also the mean rotational displacement of both implants, suggesting a higher degree of precision.ConclusionsOur study provides some evidence that PSI can improve the ability of novice surgeons to replicate a pre-operative plan, but our results suggest the need for larger-scale clinical studies to establish the role of PSI in this procedure.

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

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. 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. 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 8.1years (SD±4.6years). The mean age at the time of the Bi-UKA was 77.1years (SD±6.5years). The median hospital stay was 3 (range 2-9days) days, and the mean follow-up after Bi-UKA was 4years (SD±1.9years). 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. These results suggest that addition of a lateral UKA for arthritis progression following medial UKA is a good option in appropriately selected patients. Observational study without controls, Level IV.

Patient-specific implants for lateral unicompartmental knee arthroplasty

The lateral compartment of the knee is biomechanically and anatomically different from the medial compartment. Most commercially available unicompartmental implants are not designed specifically for the lateral compartment. Patient-specific custom-made unicompartmental knee arthroplasty (UKA) are designed to provide optimal fit on both femoral and tibial surfaces. This study aimed to determine if the use of patient-specific lateral unicompartmental implants provide better bone coverage than standard, off-the-shelf commercially available unicompartmental implants in lateral unicompartmental knee arthroplasties. As a secondary question, we wished to determine if patient-specific unicompartmental implants provide good clinical outcomes in surgical treatment of lateral unicompartmental osteoarthritis. We prospectively evaluated 33 patients who underwent lateral unicompartmental arthroplasty using patient-specific implants and instrumentation with a minimum of 24 months of follow-up. We analysed bone coverage observed in plain radiographs in 33 patient-specific lateral unicompartmental arthroplasties and compared to 20 lateral unicompartmental arthroplasties performed with commercially-available, standard off-the-shelf unicondylar implants. The mean tibial implant lateral coverage mismatch in the patient-specific implant group was 1.0 mm (S.D. 1.2, range 0-5.7 mm ) versus 3.3 mm (S.D. 2.43, range 0.4-7.8 mm) in the conventional implant group (p < 0.01). In the patient specific cohort, pre-operative limb alignment was 3.3 (valgus) and post-operative limb alignment was -0.9 (varus). The Knee Society score improved from 48 (S.D. 16.2) to 95 (S.D. 7.6). Survivorship in the patient-specific implant group was 97% at an average follow up of 37 months, versus 85% at a follow-up period of 32 months for the standard implant group. Patient-specific lateral unicompartmental knee replacements demonstrated better tibial coverage and provide excellent short-term clinical and radiological results as compared to a standard lateral UKA.

The mid-term outcomes of the Oxford Domed Lateral unicompartmental knee replacement

Mobile-bearing unicompartmental knee replacements (UKRs) with a flat tibial plateau have not performed well in the lateral compartment, owing to a high dislocation rate. This led to the development of the Domed Lateral Oxford UKR (Domed OUKR) with a biconcave bearing. The aim of this study was to assess the survival and clinical outcomes of the Domed OUKR in a large patient cohort in the medium term. We prospectively evaluated 265 consecutive knees with isolated disease of the lateral compartment and a mean age at surgery of 64 years (32 to 90). At a mean follow-up of four years (sd 2.2, (0.5 to 8.3)) the mean Oxford knee score was 40 out of 48 (sd 7.4). A total of 12 knees (4.5%) [corrected] had re-operations, of which four (1.5%) were for dislocation. All dislocations occurred in the first two years. Two (0.8%) were secondary to significant trauma that resulted in ruptured ligaments, and two (0.8%) were spontaneous. In four patients (1.5%) the UKR was converted to a primary TKR. Survival at eight years, with failure defined as any revision, was 92.1% (95% confidence interval 81.3 to 100). The Domed Lateral OUKR gives good clinical outcomes, low re-operation and revision rates and a low dislocation rate in patients with isolated lateral compartmental disease, in the hands of the designer surgeons.

Early Results of Lateral Unicompartmental Knee Replacements: A Comparison of Fixed and Mobile Bearing Prosthesis

Early Results of Lateral Unicompartmental Knee Replacements: A Comparison of Fixed and Mobile Bearing Prosthesis