The Effect of Posterior Tibial Slope on Joint Gap and Range of Knee Motion in Mobile-Bearing Unicompartmental Knee Arthroplasty

Propensity of the tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in Oxford unicompartmental knee arthroplasty: retrospective study

PURPOSE

A well-balanced joint gap is necessary in Oxford unicompartmental knee arthroplasty (OUKA) to prevent mobile-bearing dislocation. While the gaps between 20° (extension) and 100° (flexion) are precisely adjusted using the incremental mill system, there has been insufficient evaluation of gaps in other angles. We hypothesized that the gap is not always the same in other angles. This retrospective study aimed to evaluate the gap in full-extension (0°), mid-flexion (60°) and deep flexion (130°) for comparison with those in extension and flexion gaps.

METHODS

We evaluated 119 knees in 83 patients (51 females, 31 males, aged 71.9 years). The full-extension and mid-flexion gaps were compared with the extension gap, and the deep flexion gap was contrasted with the flexion gap. Each gap was classified into isometric, tight or loose, for evaluation of contributing factors.

RESULTS

Although the full-extension gap tended to be isometric (45%), the mid-flexion tended to be tight (48%), whereas the deep-flexion was loose in most knees (84%) (P = 0.002). The tight mid-flexion and loose deep flexion gap pattern accounted for 44% of the total knees, especially so with smaller femoral components (P = 0.004).

CONCLUSION

Our results highlight the propensity of tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in OUKA. Although the effect of such a minor gap imbalance is still unknown, the pattern was more prevalent in patients with smaller-sized femoral components. Use of a larger femoral component may equalize the gap throughout the motion arc.

Is combined robotically assisted unicompartmental knee arthroplasty and anterior cruciate ligament reconstruction a good solution for the young arthritic knee?

PURPOSE

Anterior cruciate ligament (ACL) deficiency can be a consequence or a cause of femoro-tibial osteoarthritis (OA). Several studies have published satisfactory outcomes of unicompartimental knee arthroplasty (UKA) and combined ACL reconstruction despite its absence classically being considered a contraindication. A major challenge in the ACL deficient knee is obtaining appropriate gap balancing and limb axis. Robotically assisted UKA allows for precise control of these factors; however, it's utilisation as a tool with combined ACL reconstruction and UKA has not been described. The purpose of this study was to evaluate the clinical and radiological outcomes of robotically assisted UKA with combined ACL reconstruction.

METHODS

This was a retrospective single-centre study of ten patients operated by a single surgeon from 2016 to 2020. All surgery was performed using a cemented fixed bearing UKA prosthesis (Journey uni, Smith and Nephew®) (8 medial, 2 lateral) inserted with the assistance of an image-free robotic-assisted system (BlueBelt, Navio, Smith and Nephew®). All ACL reconstructions were performed using hamstring autograft. Clinical assessment included International Knee Score (IKS) score, Tegner score and patient satisfaction. Radiological assessment was performed to assess radiolucent lines, progression of OA in the other compartments, Hip-Knee-Ankle angle and Posterior Tibial Slope.

RESULTS

There were eight females (80%), mean age was 57 ± 7 [48-70], mean BMI was 26 ± 3 [22-31]. The mean follow-up was 45 months ± 13 months [24-66]. Mean post-operative IKS knee and function score were respectively 96 ± 4.5 [88-100] and 93 ± 8.2 [74-100], mean Tegner score was 4.5 ± 1.4 [3-6]. Nine patients (90%) returned to sport; one patient (10%) was dissatisfied because of residual pain preventing a return to a desired level of sport. 100% of the radiological objectives were achieved. No radiolucent lines were seen at the last follow-up. There were two re-operations (20%) for stiffness requiring arthroscopic arthrolysis at two and three months respectively following surgery, with full recovery of the flexion at the last follow-up in both cases. No other complications were observed.

CONCLUSION

Robotic UKA associated with ACL reconstruction provides satisfactory early patient outcomes and accurate implant positioning. The first results in terms of return to sports were promising.

Is proximal tibial tubercle osteotomy superior to distal tibial tubercle osteotomy for medial compartmental osteoarthritis? A meta-analysis

BACKGROUND

Open-wedge high tibial osteotomy (OWHTO) is commonly performed for the treatment of medial compartment knee osteoarthritis (KOA), and is classified into proximal tibial tubercle osteotomy (PTO) and distal tibial tubercle osteotomy (DTO). The PTO osteotomy point is generally located about 3-4 cm below the joint of the proximal tibia, and the osteotomy line points to the upper part of the proximal tibiofibular joint. The DTO osteotomy point is generally located about 0.5-1.0 cm below the tibial tubercle, and the osteotomy line points to the contralateral cortex. However, there is currently no consensus on which surgical technique is superior. The purpose of our study was to investigate which among the two is superior for medial KOA, with respect to knee joint parameters, clinical function, and complications.

METHODS

This study was conducted as per the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The Cochrane Central Library, MEDLINE, Embase, PubMed, CNKI, and WanFang databases were systematically searched for trials comparing PTO and DTO in patients with medial compartment KOA, from inception until March 2022. The meta-analysis was conducted using RevMan 5.2 software. The Cochrane risk-of-bias tool was used to assess methodological quality. Statistical analysis was performed with Stata 12.0. Outcomes of interest included the Insall-Salvati index (ISI), Caton-Deschamps index (CDI), Blackburne-Peel index (BPI), posterior tibial slope (PTS), and the Hospital for Special Surgery (HSS) knee-rating scale.

RESULTS

A total of 15 retrospective studies (910 knees) were included. There were no significant differences in the age or sex of included patients. There was a significant difference in the ISI, CDI, BPI, and PTS between the two groups (all p ≤ 0.05). Further, DTO was associated with a significantly greater number of postoperative complications (p < 0.05) compared to PTO. However, there was no significant difference in the femorotibial angle (FTA), mechanical medial proximal tibial angle (mMPTA), and HSS knee score (all p > 0.05).

CONCLUSIONS

Compared with DTO, PTO is associated with a greater incidence of postoperative patella baja and increased PTS, whereas DTO is associated with more postoperative complications. Nevertheless, both can significantly correct knee varus deformity and improve knee function; their early knee function scores are also similar.

TRIAL REGISTRATION

Prospective Register of Systematic Reviews (PROSPERO) registration number CRD42021284443.

No Difference Unicompartmental Knee Arthroplasty for Medial Knee Osteoarthritis With or Without Anterior Cruciate Ligament Deficiency: A Systematic Review and Meta-analysis

BACKGROUND

A functional intact anterior cruciate ligament (ACLI) is considered to be a prerequisite for unicompartmental knee arthroplasty (UKA). However, UKA has been shown to have good clinical efficacy in ACL-deficient (ACLD) knees at 3 to 10 years follow-up. Therefore, the role of ACLD in UKA remains controversial, and more evidence is needed to clarify the role of ACLD in UKA.

METHODS

PubMed, the Web of Science, EMBASE, and Cochrane Central were queried for articles comparing the results of the ACLD and ACLI groups after UKA. Outcomes of interest included the Tegner Activity Scale, the Oxford Knee Score (OKS), postoperative slope of the implant (PSI), the Knee Injury and Osteoarthritis Outcomes Score (KOOS), the Lysholm score, and revision rate. There were eight studies included. The mean age was 66 years (range 49 to 87 year old) and the mean follow-up time was 6.9 years (range 1.3 to 16.6 years). There was baseline comparability regarding mean age, duration of follow-up, and body mass index (P > .5) between the ACLD and ACLI groups.

RESULTS

The ACLD and ACLI groups had improved postoperative functional indicators, and that postoperative revision rate (mean difference [MD], 1.24; 95% confidence interval [CI], 0.75 to 2.04; P = .4), Tegner score (MD, -0.1; 95% CI, -0.26 to 0.05; P = .19), and Lysholm score (95% CI, -2.46 to 7.32; P = .33) were similar between the groups, with no significant differences; however, the ACLD groups had significantly better KOOS Activities of Daily Living scores, with a significant difference (MD, 4.53; 95% CI, 1.75 to 7.3; P = .001). Also, there were no significant differences between two groups in the PSI, OKS, KOOS.

CONCLUSION

ACL deficiency is not always a contraindication for UKA. With correct patient selection, UKA could be considered for medial knee osteoarthritis with ACL deficiency without antero-posterior instability, especially these people over 60 years of age.

Radiographic and Clinical Evolution of the Oxford Unicompartmental Knee Arthroplasty

The aim of the study is to evaluate whether the use of the new instrumentation Microplasty (MP) improves component positioning and the reliability of the surgical technique, reducing the implant outliers from the recommended range and providing a more accurate resection, while avoiding insufficient or excessive tibial resection and clinical scores. We prospectively analyzed clinical and radiographic outcomes of three consecutive cohorts for a total of 227 implants at a minimum follow-up of 36 months. The first cohort consisted of 67 Oxford unicompartmental knee arthroplasty (OUKA), using the phase III (Ph-III). The second cohort consisted of 136 OUKA, with the MP instrumentation. The third cohort consisted of 24 hypoallergenic OUKA, using the MP instrumentation (TiNbN). Postoperative alignment of the knee in the coronal and sagittal plane was measured using radiographs. No clinical differences were found among the three groups (p > 0.05). A significant difference was found on the slope between Ph-III and MP (p = 0.0005). Moreover, a significant difference was found in tibial angle and in tibial slope in arthroplasty with femoral size small (S), compared with size medium (M) or large (Ly) (tibia varus/valugs angle: p = 0.0484; tibial slope: p = 0.04). Similar results were found between small (AA, A, B) tibial size and large (C, D, E, F) tibial size for tibial varus/valgus (p = 0.03) angle and tibial slope (p = 0.003). A significant difference was found between Ph-III and MP in tibial slope in patients with body mass index (BMI) ≥25 kg/m² (p = 0.0003). A positive correlation was noted between the femoral and tibial sizes and the tibial angle and the slope, and a negative correlation between weight and the tibial slope; furthermore, a positive correlation was found between Oxford knee score and radiographic angles. The MP instrumentation seems to be effective in determining the tibial cut and, particularly, improving the tibial slope, compared with Ph-III. The tibial slope is directly affected by the weight and measurements of the components, regardless of the instruments or the number of pegs, while clinical outcomes are correlated with implant position. This prospective comparative study reflects level of evidence II.

A direct referencing method of the tibial plateau for the posterior tibial slope in medial unicompartmental knee arthroplasty

PURPOSE

There is no consensus on intraoperative references for the posterior tibial slope (PTS) in medial unicompartmental knee arthroplasty (UKA). An arthroscopic hook probe placed on the medial second quarter of the medial tibial plateau (MTP) in an anteroposterior direction may be used as a direct anatomical reference for the PTS. The purpose of this study is to investigate the availability and accuracy of this method.

METHODS

Marginal osteophyte formation and subchondral depression of the MTP and angles between the bony MTP and the cartilage MTP were retrospectively evaluated using preoperative sagittal MRI of 73 knees undergoing medial UKA. In another 36 knees, intraoperative lateral knee radiographs with the probe placed on the MTP were prospectively taken in addition to the preoperative MRI. Then, angles between the bony MTP and the probe axis and angles between the preoperative bony MTP and the postoperative implant MTP were measured.

RESULTS

Among 73 knees, one knee with grade 4 osteoarthritis had a posterior osteophyte higher than the most prominent point of the cartilage MTP. No subchondral depression affected the direct reference of the MTP. The mean angle between the bony MTP and the cartilage MTP was -0.8° ± 0.7° (-2.6°-1.0°, n = 72), excluding one knee with a "high" osteophyte. The mean angle between the bony MTP and the probe axis on the intraoperative radiograph was -0.6° ± 0.4° (-1.7-0.0, n = 36). The mean angle between the pre- and postoperative MTP was -0.5° ± 1.5° (-2.9°-1.8°). The root-mean-square (RMS) error of these two PTS angles was 1.6° with this method.

CONCLUSION

Cartilage remnants, osteophyte formation and subchondral bone depression do not affect the direct referencing method in almost all knees for which medial UKA is indicated. When the posterior "high" osteophyte of the MTP is noted on preoperative radiography, preoperative MRI or CT scan is recommended to confirm no "high" osteophyte on the medial second quarter. The accuracy of this method seems equal to that of robotic-assisted surgery (the RMS error in previous reports, 1.6°-1.9°).

Posterior condylar offset and posterior tibial slope targets to optimize knee flexion after unicompartmental knee arthroplasty

PURPOSE

To evaluate the relationship between posterior tibial slope (PTS), posterior condylar offset (PCO), femoral sagittal angle (FSA) on clinical outcomes, and propose optimal sagittal plane alignments for unicompartmental knee arthroplasty (UKA).

METHODS

Prospectively collected data of 265 medial UKA was analysed. PTS, PCO, FSA were measured on preoperative and postoperative lateral radiographs. Clinical assessment was done at 6-month, 2-year and 10-year using Oxford Knee Score, Knee Society Knee and Function scores, Short Form-36, range of motion (ROM), fulfilment of satisfaction and expectations. Implant survivorship was noted at mean 15-year. Kendall rank correlation test evaluated correlations of sagittal parameters against clinical outcomes. Multivariable linear regression evaluated predictors of postoperative ROM. Effect plots and interaction plots were used to identify angles with the best outcomes. (p < 0.05) was the threshold for statistical significance.

RESULTS

There were significant correlations between PTS, PCO and FSA. Younger age, lower BMI, implant type, greater preoperative flexion, steeper PTS and preservation of PCO were significant predictors of greater postoperative flexion. There were significant interaction effects between PTS and PCO. Effect plots demonstrate a PTS between 2° to 8° and restoration of PCO within 1.5 mm of native values are optimal for better postoperative flexion. Interaction plot reveals that it is preferable to reduce PCO by 1.0 mm when PTS is 2° and restore PCO at 0 mm when PTS is 8°.

CONCLUSION

UKA surgeons and future studies should be mindful of the relationship between PTS, PCO and FSA, and avoid considering them in isolation. When deciding on the method of balancing component gaps in UKA, surgeons should rely on the PTS. Decrease the posterior condylar cut when PTS is steep, and increase the posterior condylar cut when PTS is shallow. The acceptable range for PTS is between 2° to 8° and PCO should be restored to 1.5 mm of native values.

LEVEL OF EVIDENCE

II.

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.

Intraoperative rotational kinematics and its influence on postoperative clinical outcomes differ according to age in Unicompartmental knee Arthroplasty

Background

Although Oxford unicompartmental knee arthroplasty (UKA) is used in patients of wide age ranges, there is no clear information regarding the age differences in terms of intraoperative femorotibial rotational kinematics and its influence on clinical outcomes. Therefore, this study was conducted to examine the age differences in terms of intraoperative rotational kinematics and postoperative clinical outcomes and to analyze their relationship with classification according to the age group.

Methods

We investigated 111 knees of patients who underwent Oxford UKA using a navigation system and divided them into two groups: elderly (aged ≥75 years; 48 knees) and nonelderly (aged < 75 years; 63 knees). Intraoperative tibial internal rotational angles relative to the femur during passive knee flexion were measured using a navigation system, and clinical outcomes were evaluated using knee range of motion, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and the Knee Society Functional Score at 2 years postoperatively. The relationships between intraoperative tibiofemoral rotational angles and clinical outcomes were also evaluated in the two groups.

Results

The intraoperative tibial internal rotational angle relative to the femur during knee flexion was significantly larger in the nonelderly group (13.5°) than in the elderly group (9.0°). The intraoperative tibial internal rotational angle showed a positive correlation with the pain subscale of KOOS only in the nonelderly group.

Conclusion

Intraoperative rotational kinematics and its influence on clinical outcomes were different between elderly and nonelderly patients, and the tibial internal rotational angle could be a more important factor for successful UKA in nonelderly patients.

Extent of in vivo sagittal bearing movement and its relationship with tibial posterior slopes in Oxford mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

The effect of increased tibial slope on the bearing movement and clinical results in mobile-bearing unicompartmental knee arthroplasty has not been well discussed. We aimed to clarify the extent of in vivo sagittal bearing movement and bearing overhang using fluoroscopy and their relationship with the tibial posterior slopes and clinical results.

METHODS

This retrospective study included 40 patients who underwent Oxford unicompartmental knee arthroplasty for anteromedial osteoarthritis or osteonecrosis of the knee. Intraoperative posterior translation and posterior overhang of the bearing were assessed during flexion. The tibial posterior slopes were evaluated before and 2 weeks after surgery, and its increment was recorded. Clinical evaluations were also performed preoperatively and at 2 years postoperatively (maximum flexion angle, Oxford Knee Score). Single linear regression analysis was performed to assess the correlation between the tibial posterior slopes and the posterior translation and the posterior overhang and determine if these could affect the clinical outcomes.

FINDINGS

The average posterior translation was 10.7 ± 4.3 mm, and posterior overhang of the mobile bearing was found in 35% of overall patients. They were associated with increased tibial slope as well as poorer improvement in Oxford Knee Score at 2 years postoperatively.

INTERPRETATION

In Oxford unicompartmental knee arthroplasty, mobile bearing can probably move posteriorly beyond the posterior margin of the tibial component during flexion when the tibial posterior slope increases more than the original magnitude. Additionally, the posterior translation and posterior overhang closely correlated with the poorer improvement in Oxford Knee Score at 2 years postoperatively.

A real 3D measurement technique for the tibial slope: differentiation between different articular surfaces and comparison to radiographic slope measurement

Background

The tibial slope plays an important role in knee surgery. However, standard radiographic measurement techniques have a low reproducibility and do not allow differentiation between medial and lateral articular surfaces. Despite availability of three-dimensional imaging, so far, no real 3D measurement technique was introduced and compared to radiographic measurement, which were the purposes of this study.

Methods

Computed tomography scans of 54 knees in 51 patients (41 males and 10 females) with a mean age of 46 years (range 22–67 years) were included. A novel 3D measurement technique was applied by two readers to measure the tibial slope of medial and lateral tibial plateau and rim. A statistical analysis was conducted to determine the intraclass correlation coefficient (ICC) for the new technique and compare it to a standard radiographic measurement.

Results

The mean 3D tibial slope for the medial plateau and rim was 7.4° and 7.6°, for the lateral plateau and rim 7.5° and 8.1°, respectively. The mean radiographic slope was 6.0°. Statistical analysis showed an ICC between both readers of 0.909, 0.987, 0.918, 0.893, for the 3D measurement of medial plateau, medial rim, lateral plateau and lateral rim, respectively, whereas the radiographic technique showed an ICC of 0.733.

Conclusions

The proposed novel measurement technique shows a high intraclass agreement and offers an applicable opportunity to assess the tibial slope three-dimensionally. Furthermore, the medial and lateral articular surfaces can be measured separately and one can differentiate the slope from the plateau and from the rim. As three-dimensional planning becomes successively more important, our measurement technique might deliver a useful supplement to the standard radiographic assessment in slope related knee surgery.

Level of evidence

Level III, diagnostic study.