Unicondylar Knee Arthroplasty

Severe Lateral Facet Patella Osteoarthritis Is Not Associated With Increased Failure at Mean 10 Years After Lateral Unicompartmental Knee Arthroplasty

BACKGROUND

The purpose of this study was to determine if severe lateral patella facet osteoarthritis was related to lower survivorship and poor patient-reported outcomes following fixed-bearing lateral unicompartmental knee arthroplasty (UKA).

METHODS

There were 61 patients who underwent a fixed-bearing, nonrobotically assisted, lateral UKA between May 7, 2003 and December 18, 2019 and met the inclusion criteria. The patello-femoral joint was examined intraoperatively for chondral damage prior to UKA implantation. Severe lateral facet patella osteoarthritis (LFPOA) was defined as Outerbridge grades 3 or 4 changes on the lateral facet. All patients completed subjective functional outcomes questionnaires and a clinical examination at a minimum of 4 years following UKA.

RESULTS

Severe LFPOA was identified in 28 (46%) patients. At a mean follow-up of 10.9 years, there were no statistically significant differences in any Knee Osteoarthritis Outcomes Score (KOOS) subscale or Kujala scores between patients who had and did not have severe LFPOA. There was no statistically significant difference in the percentage of patients who achieved Patient Acceptable Symptom State for the KOOS subscale scores between groups. Mean survival in patients who did not have severe LFPOA was 16.6 years (95% confidence interval, 15.4 to 17.7) compared to 18.9 years (95% confidence interval, 17.6 to 20.2) in patients who had severe LFPOA (P = 0.62).

CONCLUSIONS

Severe LFPOA did not result in lower survival or inferior functional outcomes compared to patients who did not have severe osteoarthritis at an average 10-year follow-up after fixed-bearing lateral UKA.

Fixed-Bearing Lateral Unicompartment Knee Arthroplasty in Degenerative ACL-Deficient and ACL-Intact Knees: A Matched Pair Analysis

BACKGROUND

Anterior cruciate ligament (ACL)-deficient knees are no longer considered a contra-indication for unicompartment knee arthroplasty (UKA). The purpose of this study was to determine if patients who had an ACL-deficient knee who underwent lateral UKA had similar mean 10-year outcomes compared to patients who had an ACL-intact knee and lateral UKA.

METHODS

Patients who underwent a lateral UKA with ACL deficiency by a single surgeon between 2004 and 2016 were identified. Preoperative magnetic resonance images were utilized to identify a torn or absent ACL in all knees. The absence of an ACL was confirmed during arthroscopy prior to UKA. Patients were matched 1:2 based on age and sex with patients who underwent lateral UKA with an ACL intact knee. The primary patient-reported outcome variable was survival without conversion to total knee arthroplasty. Secondary outcomes included Veterans Rand-12, the Lysholm score, the Knee Osteoarthritis Outcome Score activities of daily living subscale, and Sport subscale. A power analysis showed that 14 patients were needed to identify differences of 10 points on the Knee Osteoarthritis Outcome Score with a power of 80% (P = .05).

RESULTS

The cohort of patients who had an ACL-deficient lateral UKA included 4 men and 12 women (43 to 82 years of age). The matched control group included 32 patients. The mean age of both groups was 67 years (range, 43 to 85). There were 2 patients in the ACL-deficient group who failed. At 10 years, survivorship in the ACL-deficient group was 85%, while survival in the ACL-intact group was 100% (P = .035). At an average follow-up of 11 years (range, 4 to 19.6), there was no difference in outcome scores between ACL-deficient and ACL-intact patients.

CONCLUSION

Fixed-bearing lateral UKA in the ACL-deficient knee resulted in lower survival than patients who had an intact ACL. Patient-reported outcomes were similar in both groups. The ACL-deficient patient who wishes to undergo lateral UKA should be counseled on the lower survival.

LEVEL OF EVIDENCE

Level III. Retrospective cohort study.

Biomechanical effects of femoral prosthesis misalignment on the structure of the lateral compartment during medial unicompartmental knee arthroplasty in osteoporotic patients

BACKGROUND

This study aims to investigate the impact of varying coronal alignments of femoral prostheses on stress and strain distributions within the lateral compartment following unicompartmental knee arthroplasty (UKA) in patients with normal bone density and osteoporosis using finite element analysis. Additionally, it examines the relationship between osteoporosis and the progression of osteoarthritis in the lateral compartment postoperatively.

METHODS

UKA models were developed for both normal bone and osteoporotic conditions using a validated finite element model of the knee. Seven alignment conditions for the femoral prosthesis were simulated: 0° (neutral alignment), varus angles of 3°, 6°, and 9°, and valgus angles of 3°, 6°, and 9°, resulting in a total of 14 scenarios. Stress and strain distributions in the meniscus, tibial cartilage, and femoral cartilage of the lateral compartment were evaluated.

RESULTS

The results indicated that stress and strain in the meniscus, tibial cartilage, and femoral cartilage of the lateral compartment increased with greater varus alignment and decreased with greater valgus alignment in both normal and osteoporotic models. At equivalent alignment angles, stress and strain were consistently higher in the osteoporotic model (M2) compared to the normal bone model (M1), although the peak equivalent stress in the tibial cartilage was lower in the M2 model than in the M1 model.

CONCLUSIONS

In patients with osteoporosis undergoing fixed-bearing medial UKA, varus malalignment of the femoral prosthesis can lead to increased stress and strain in the lateral compartment's meniscus, tibial cartilage, and femoral cartilage. These findings suggest that osteoporosis may contribute to abnormal stress and strain distributions in the lateral compartment following UKA, potentially accelerating the progression of osteoarthritis in this region postoperatively.

Unicompartmental knee arthroplasty improves mental health in patients with single compartment knee osteoarthritis

PURPOSE

The purpose of this study was to determine if preoperative mental health status improves following unicompartmental knee arthroplasty (UKA) in patients with single compartment knee osteoarthritis (OA).

METHODS

A total of 163 patients underwent UKA [115 (71%) medial, 48 (29%) lateral] (mean age = 65 ± 11) completed preoperative and minimum 2-year postoperative veterans RAND 12 item health survey (VR-12) mental component score (MCS). VR-12 MCS was the primary outcome measure. Secondary measures included VR-12 physical component summary score (PCS), knee osteoarthritis outcome score (KOOS) and KOOS patient acceptable symptom state at the final follow-up.

RESULTS

The median VR-12 MCS improved from 50.5 [interquartile range (IQR): 43.7-56.8] to 55.0 [IQR: 52.3-57.0] (p < 0.001) at a mean follow-up of 9.5 ± 4 years (range 2-19 years) following UKA. Preoperative VR-12 MCS was significantly correlated with patients postoperative VR-12 PCS (ρ = 0.294, p < 0.01), KOOS pain (ρ = 0.201, p = 0.012), KOOS ADL (ρ = 0.243, p = 0.002) and KOOS quality of life (ρ = 0.233, p < 0.01). Sixty-three (39%) patients improved from low VR-12 MCS (<50) to normal VR-12 MCS (≥50). One hundred forty-two (87%) achieved a normal VR-12 MCS score (≥50) postoperatively.

CONCLUSION

At a mean of 10-year follow-up, patients who underwent UKA for single compartment osteoarthritic knee pain demonstrated significant improvement in mental health scores. UKA resulted in normal mental health in a majority of patients (87%). The resultant improved mental health scores were associated with improved patient pain and activities of daily living.

LEVEL OF EVIDENCE

Level III retrospective cohort study.

Impact of lateral meniscus injury detected by preoperative magnetic resonance imaging on midterm results after unicompartmental knee arthroplasty

BACKGROUND

The significance of lateral meniscus injury and its impact on success rates with medial unicompartmental knee arthroplasty (UKA) is still debated among scholars. This study aims to investigate whether preoperative magnetic resonance imaging (MRI) findings of lateral meniscus injury influence midterm outcomes following UKA.

METHODS

This study recruited 104 patients who underwent medial mobile-bearing UKA. Based on the extent of lateral meniscus injury indicated by the preoperative MRI and Stoller's classification system, patients were divided into two groups: the normal group (grade 0), and the lateral meniscus injury group (grade 3). Further, preoperative demographic and clinical outcome data (Hospital for Special Surgery score, lateral knee pain, squatting, and knee extension ability) were compared at least 2 years postoperatively.

RESULTS

No statistically significant difference in knee function or clinical outcome was found between the normal group (n = 59) and the lateral meniscus injury group (n = 45). During the 39.2 months (range: 24-64 months), no patient required any reoperation or revision procedures.

CONCLUSION

In summary, the presence of lateral meniscus injury as determined by preoperative MRI does not affect the midterm results after UKA. Without additional treatment for lateral meniscus injury, UKA can yield desired outcomes regardless of the presence of lateral meniscus injury on preoperative MRI.

The Role of Severe Lateral Facet Patellar Osteoarthritis in Patient Selection for Success of a Medial Unicompartmental Knee Arthroplasty: Mean Follow-Up of 10 Years

BACKGROUND

Lateral facet patellar osteoarthritis (LFPOA) has been reported as a contraindication for medial unicompartmental (UKA). The purpose of this paper was to determine if severe LFPOA was related to lower survivorship and patient-reported outcomes following medial UKA.

METHODS

A total of 170 medial UKAs were performed. Severe LFPOA was defined as Outerbridge grade 3 to 4 damage on the lateral facet cartilage surfaces of the patella as noted intraoperatively. There were 122 of 170 patients (72%) who had noLFPOA and 48 of 170 patients (28%) who had had severe LFPOA. A routine patelloplasty was performed in all patients. Patients completed the Veterans RAND 12-Item Health Survey (VR-12) Mental Component Score (MCS) and Physical Component Score (PCS), Knee Injury and Osteoarthritis Outcome Score (KOOS), and Knee Society Score.

RESULTS

There were 4 patients in the noLFPOA group who required total knee arthroplasty and 2 in the LFPOA group. There was no significant difference in mean survival time: noLFPOA = 17.2 years [95% confidence interval (CI): 17 to 18] and LFPOA = 18.0 years [95% CI: 17 to 19] (P = .94). At mean follow-up of 10 years, there were no significant differences in knee flexion or extension. Patello-femoral crepitus without pain was noted in 7 patients who had LFPOA and 21 patients who had noLFPOA. There were no significant differences in VR-12 MCS, PCS, KOOS subscales, or Knee Society Score between groups. Patient acceptable symptom state (PASS) was achieved in 80% (90 of 112) for KOOS ADL in the noLFPOA group and 82% (36 of 44) in the LFPOA group (P = .68). PASS was achieved in 82% (92 of 112) for KOOS Sport in the noLFPOA group and 82% (36/44) in the LFPOA group (P = .87).

CONCLUSION

At a mean of 10 years, patients who had LFPOA had equivalent survivorship and functional outcomes to patients who did not have LFPOA. These long-term results suggest that asymptomatic grade 3 or 4 LFPOA is not a contraindication to medial UKA.

Isolated Lateral Tibiofemoral Compartment Osteoarthritis: Survivorship and Patient Acceptable Symptom State After Lateral Fixed-Bearing Unicompartmental Knee Arthroplasty at Mean 10-Year Follow-up

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) is an excellent option to alleviate disability and restore function in patients with lateral compartment knee osteoarthritis (OA). The purpose of the present study was to determine the survivorship and long-term outcomes in both younger/middle-aged and older patients with lateral compartment OA following non-robotically-assisted, fixed-bearing lateral UKA and to determine if an acceptable symptom state can be achieved.

METHODS

All patients were managed with fixed-bearing lateral UKA by a single surgeon utilizing a lateral parapatellar approach without robotic assistance. The primary outcome variables were the Knee injury and Osteoarthritis Outcome Score (KOOS) Activities of Daily Living (ADL) and Sport subscale scores. In addition, the other KOOS subscores, the Lysholm score, the achievement of the Patient Acceptable Symptom State (PASS), and the Veterans RAND (VR-12) Physical Component Summary score (PCS) and Mental Component Summary score (MCS) were collected. Failure was defined as conversion to total knee arthroplasty (TKA). Patients were divided into 2 cohorts: younger/middle-aged patients (<60 years of age) and older patients (≥60 years of age).

RESULTS

A cohort of 256 patients underwent medial (n = 193) or lateral (n = 63) UKA. Sixty-one patients met the inclusion criteria. At mean of 10 years (range, 4 to 17 years) of follow-up, there were no significant differences between the groups in terms of any patient-reported outcome measures (p > 0.05). The percentage of patients in whom PASS was achieved on the KOOS ADL and Sport subscores was 82% and 88%, respectively, in the younger cohort and 80% and 80%, respectively, in the older cohort. The mean survival estimate of the prothesis was 15.3 years (95% confidence interval [CI], 14.5 to 16.2 years) for the entire cohort. The estimated rate of implant survival in the younger cohort was 100% at 5 and 10 years, and the estimated rate of implant survival in the older cohort was 98% at 5 years and 96% at 10 years.

CONCLUSIONS

Lateral fixed-bearing, non-robotic UKA for the treatment of isolated lateral compartment OA resulted in >80% of patients reaching an acceptable symptom state in terms of both activities of daily living and sporting activities. UKA provides an excellent option that provides longevity with high PASS rates and return to activities with a low risk of complications and failure.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

The Lawrence D. Dorr Surgical Techniques & Technologies Award: Patient Acceptable Symptom State (PASS) in Medial and Lateral Unicompartmental Knee Arthroplasty: Does the Status of the ACL Impact Outcomes?

BACKGROUND

The aim of this study is to determine if there is a difference in the percentage of patients who reach Patient Acceptable Symptom State (PASS) when comparing anterior cruciate ligament (ACL)-deficient and ACL-intact knees following fixed-bearing medial and lateral unicompartmental knee arthroplasty (UKA).

METHODS

A consecutive series of 215 knees that underwent UKA (medial = 158, lateral = 57) were included in the study. The Knee Osteoarthritis Outcome Score functional score [KOOS activities of daily living (ADL)] and KOOS Sport were used as the primary outcome variables. A KOOS ADL PASS of 87.5 and KOOS Sport PASS of 43.8 were previously described for total knee arthroplasty (TKA). Failure was defined as conversion to TKA.

RESULTS

There were 157 in the ACL-intact group and 58 in the ACL-deficient group. Conversion to TKA was 3.7%. The failure rate in the ACL-deficient group was 5% (3/58) and 3% (5/157) in the ACL-intact group (P = .447). The mean survival for the entire group was 18.1 years (95% confidence interval 17.6-18.6). At 10 years, the survival was 94.3% (standard error = 0.028) in the ACL-deficient group and 97.6% (standard error = 0.014) in the ACL-intact group. At a mean 10 ± 3.5 years, with 93% follow-up, 83% in the ACL-deficient group and 80% in the ACL-intact group reached PASS for KOOS ADL (P = .218). For KOOS Sport, 85% of the ACL-deficient group compared to 81% in the ACL-intact group (P = .374) reached PASS.

CONCLUSION

The ACL-deficient cohort results were not significantly different compared to ACL-intact knees in both medial and lateral compartment UKA. Fixed-bearing medial and lateral UKA resulted in low failure rate and excellent long-term outcomes.

Pre-Arthritic/Kinematic Alignment in Fixed-Bearing Medial Unicompartmental Knee Arthroplasty Results in Return to Activity at Mean 10-Year Follow-up

BACKGROUND

The optimal alignment strategy in unicompartmental knee arthroplasty (UKA) is debated. Recent studies have suggested that kinematic alignment may lead to improved biomechanics and outcomes. The aim of the present study was to determine if pre-arthritic/kinematic alignment of knees would result in sustained long-term restoration of function, without conversion to total knee arthroplasty (TKA), following non-robotically assisted, fixed-bearing medial UKA.

METHODS

A total of 236 UKAs were performed from 2000 to 2015. Of these, a total of 150 medial UKAs met the inclusion criteria and were included in the study. There were 76 UKAs performed in female patients. The mean age was 65 ± 10 years and the mean body mass index was 28.6 ± 5 kg/m2. Patients with ≥15° of varus alignment preoperatively were excluded. Varus deformity was evaluated with use of the hip-knee-ankle angle (HKAA). Pre-arthritic/kinematic alignment was estimated with use of an arithmetic HKAA (aHKA, calculated as the medial proximal tibial angle minus the lateral distal femoral angle). We defined pre-arthritic/kinematic alignment as a postoperative HKAA within 3° of the aHKA. The primary outcome measures were the Knee Injury and Osteoarthritis Outcome Score (KOOS) Activities of Daily Living and Sport subscales, including the percentage of patients who met the patient acceptable symptom state (PASS) for these measures. Failure was defined as conversion to TKA.

RESULTS

The mean follow-up was 10 years (range, 4 to 20 years), with a mean survival time estimate of 18.3 years (95% confidence interval [CI], 17.8 to 18.8). The rate of conversion to TKA was 3% (5 of 150 UKAs). Postoperatively, 127 (85%) of 150 knees were pre-arthritic/kinematically aligned, and 23 knees (15%) were not. Patients with compared to those without pre-arthritic/kinematically aligned knees had significantly longer mean survival (18.6 years; 95% CI, 18.2 to 19) compared with 15.4 years; 95% CI, 13.4 to 17.5, respectively; p = 0.008) and higher KOOS Activities of Daily Living (92 compared with 74; p < 0.001) and Sport subscale scores (74 compared with 36; p < 0.001). A greater proportion of knees in the pre-arthritic/kinematically aligned cohort met the PASS for the KOOS Activities of Daily Living (85%, 106 of 125 knees) and Sport subscales (109 of 125, 87%) compared with the non-pre-arthritic/kinematically aligned cohort (28% and 57%, respectively; p < 0.01).

CONCLUSIONS

Pre-arthritic/kinematically aligned knees in this non-robotically assisted fixed-bearing medial UKA cohort had superior outcomes, including the KOOS Activities of Daily Living and Sport subscales and achievement of the PASS for these measures, compared with non-pre-arthritic/kinematically aligned at an average of 10 years after UKA. Knees that fell within 3° of a simple aHKA measurement on a 3-foot (1-m)-long standing radiograph had greater longevity and return to activities.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

A Comparative Study of Total Knee Arthroplasty and Unicondylar Knee Arthroplasty in the Treatment of Knee Osteoarthritis

Objective

To compare the clinical efficacy of total knee arthroplasty (TKA) and unicondylar knee arthroplasty (UKA) in the treatment of knee osteoarthritis (KOA).

Methods

A retrospective analysis was conducted on 30 patients admitted to the Department of Orthopaedics of Yijishan Hospital from 2020 to 2021. The patients were divided into UKA group (n = 15) and TKA group (control, n = 15). The intraoperative situation and postoperative clinical indicators of patients in the two groups were collected and compared, such as operation time, intraoperative blood loss, length of hospital stay, postoperative complications, and postoperative functional recovery. Postoperative functional recovery was investigated by the visual analogue pain scale (VAS), knee score scale (HSS), and knee range of motion (ROM) scores 5 days after surgery.

Results

Perioperative indexes in the UKA group were significantly lower than those in the TKA group, including operation time, intraoperative blood loss, first time going to the ground, and length of hospital stay. VAS, HSS, and ROM scores in the two groups were significantly improved after surgery compared with those before surgery. However, ROM scores in the UKA group were significantly better than in the TKA group. In terms of early postoperative complications, there was one case of venous thrombosis of lower limbs in the UKA group, while in the TKA group there was one case of delayed wound healing due to diabetes, and one case of deep infection.

Conclusion

Both UKA and TKA are very successful options for the treatment of KOA, but the use of UKA can promote the recovery of postoperative knee function, reduce postoperative complications, and achieve more satisfactory than expected results.

Relevance of the Tibial Slope on Functional Outcomes in ACL-Deficient and ACL Intact Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Excessive posterior tibial slope in medial unicompartmental knee arthroplasty (UKA) has been implicated in early failure. The purpose of this study was to evaluate the relationship between preoperative posterior tibial slope and postoperative slope of the implant (PSI) on outcomes in patients with anterior cruciate ligament (ACL) intact and ACL-deficient knees after fixed-bearing medial UKA.

METHODS

Patients who underwent a medial UKA between 2002 and 2017 with a minimum 3-year follow-up were included. Preoperative posterior tibial slope and postoperative PSI were measured. Outcomes measures included Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales, Lysholm, and VR-12. Failure was defined as conversion to total knee arthroplasty.

RESULTS

Of 241 knees undergoing UKA, 131 patients (70 women, 61 men; average age of 65 ± 10 years (average BMI of 27.9 ± 4) were included. For all patients, survivorship was 98% at 5 years and 96% at 10 years with a mean survival time for UKA was 15.2 years [95% CI: 14.6-15.7]. No failure had a PSI >7°. There were no superficial or deep infections. There were no significant differences in outcome scores between the ACL intact and the ACL-deficient group; therefore, the data were combined for analysis. At mean 8-year follow-up, KOOS pain scores were better in patients with PSI ≤7° (87 ± 16) than those with PSI >7° (81 ± 15). 76% of patients with PSI ≤7° reached the Patient Acceptable Symptom State for KOOS pain; whereas, 59% of patients with PSI >7° reached PASS for KOOS pain (P = .015).

CONCLUSION

Patients with postoperative posterior slope of the tibial implant >7° had significantly worse postoperative pain, without conversion to TKA, and with maintenance of high function. In ACL deficient and intact knees, nonrobotically-assisted, fixed-bearing medial UKA had a 96% survivorship at 10 years.

Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees

AIMS

The patient-acceptable symptom state (PASS) is a level of wellbeing, which is measured by the patient. The aim of this study was to determine if the proportion of patients who achieved an acceptable level of function (PASS) after medial unicompartmental knee arthroplasty (UKA) was different based on the status of the anterior cruciate ligament (ACL) at the time of surgery.

METHODS

A total of 114 patients who underwent UKA for isolated medial osteoarthritis (OA) of the knee were included in the study. Their mean age was 65 years (SD 10). No patient underwent a bilateral procedure. Those who had undergone ACL reconstruction during the previous five years were excluded. The Knee injury Osteoarthritis Outcome Score Activities of Daily Living (KOOS ADL) function score was used as the primary outcome measure with a PASS of 87.5, as described for total knee arthroplasty (TKA). Patients completed all other KOOS subscales, Lysholm score, the Western Ontario and McMaster Universities Osteoarthritis Index, and the Veterans Rand 12-item health survey score. Failure was defined as conversion to TKA.

RESULTS

Survivorship at ten years was 97% in both the ACL-deficient and ACL-intact groups. The mean survival was 16.1 years (95% confidence interval (CI) 15.3 to 16.8) for the ACL-deficient group and 15.6 years (95% CI 14.8 to 16.361) for the ACL-intact group (p = 0.878). At a mean of nine years (SD 3.5) in the ACL-deficient group, 32 patients (87%) reached the PASS for the KOOS ADL. In the ACL-intact group, at a mean of 8.6 years (SD 3) follow-up, 63 patients (85%) reached PASS for the KOOS ADL. There was no significant difference in the percentage of patients who reached PASS for all KOOS subscales and Lysholm between the two groups.

CONCLUSION

PASS was achieved in 85% of all UKAs for KOOS ADL, similar to reports for TKA. Fixed-bearing, medial, non-robotically-assisted UKA resulted in 97% survival at ten years in both the ACL-deficient and ACL-intact groups. There was no significant difference in all outcomes between the two groups. Understanding PASS will allow better communication between surgeons and patients to improve the surgical management of patients with single compartment OA of the knee. This study provides mid- to long-term data supporting the use of PASS to document outcomes following UKA. PASS was met in more than 85% of patients with no differences between ACL-deficient and ACL-intact knees at a mean follow-up of nine years. Cite this article: Bone Joint J 2021;103-B(8):1367-1372.

[Imaging study on effect of femoral intramedullary guide on the alignment of femoral prosthesis in unicompartmental knee arthroplasty]

Objective

To explore the imaging features of intramedullary guide rod and its influence on the alignment of the femoral prosthesis in unicompartmental knee arthroplasty (UKA).

Methods

Between August 2016 and November 2016, 50 patients (50 knees) with primary anteromedial osteoarthritis were treated with UKA by Oxford MicroPlasty minimally invasive replacement system. There were 10 males and 40 females. The age ranged from 62 to 77 years with an average of 68.8 years. Preoperative varus and flexion deformity angles were (5.22±3.46)° and (7.42±2.65)°, respectively. The knee range of motion (ROM) was (106.85±7.62)°. The Hospital for Special Surgery (HSS) score was 68.26±4.65. The angles between the femoral intramedullary guide rod and the anatomical axis of femur on the coronal and sagittal planes, the femoral component valgus/varus angle (FCVA), the femoral component posterior slope angle (FCPSA), knee varus deformity angle, and knee flexion deformity angle were measured by intra- and post-operative X-ray films. The postoperative ROM and HSS score were measured.

Results

Intraoperative X-ray films measurement showed that the lateral side angles between femoral intramedullary guide rod and femoral anatomical axis were observed on coronal plane, and the angles ranged from 0.28 to 2.06° with an average of 0.96°. While the posterior side angles were observed on sagittal plane, and the angles ranged from 0.09 to 0.48° with an average of 0.23°. The angulations (>1°) between femoral intramedullary part guide rod and outside part of the rod were confirmed in 12 cases (24%) on coronal plane. Postoperative femoral prosthesis were mild varus in 38 patients (76%). The FCVA ranged from -1.76 to 4.08° with an average of 2.21°. The FCPSA ranged from 7.12 to 13.86° with an average of 9.16°. All patients were followed up 22-26 months, with an average of 24.5 months. The incisions healed by first intention. At last follow-up, the varus and flexion deformity angles were (1.82±1.05) and (2.54 ± 1.86)°, respectively. ROM was (124.62±5.85)° and HSS score was 91.58±3.65. There were significant differences between pre- and post-operative parameters ( P<0.05). No complication such as dislocation or aseptic loosening of the prosthesis occurred during the follow-up.

Conclusion

UKA by Oxford MicroPlasty minimally invasive replacement system can obtain accurate femoral prosthesis position with the help of intramedullary guide system, and the effectiveness is excellent.