Large variance in a lateral osteoarthritic population prior to and following lateral unicompartmental arthroplasty: An analysis of knee phenotypes.

BACKGROUND: Disagreement exists on the optimal coronal alignment target for lateral unicompartmental knee arthroplasty (UKA). An improved understanding of the distribution of coronal alignment and joint line orientation in lateral osteoarthritis (OA) might prove beneficial. The aim of this study was to evaluate the pre- and postoperative Coronal Plane Alignment of the Knee (CPAK) distribution following lateral UKA and to evaluate the association between phenotypic variation and patient-reported outcome measures (PROMs). METHODS: A surgeon's registry was retrospectively reviewed between 2012 and 2022 to identify patients who received primary lateral UKA for advanced, lateral compartment OA. Radiographic measurements were performed, and CPAK phenotypes were determined. The Knee Injury and Osteoarthritis Outcome Score (KOOS), Kujala, and patient satisfaction were analyzed at one-year and two-year follow-up. RESULTS: A total of 305 knees were included. Preoperatively, seven phenotypes were observed and CPAK3 (54.1%) was most commonly observed. Postoperatively, all nine phenotypes were observed and CPAK6 (32.8%) was predominant. Preoperatively, 23.6% did not have a prearthritic valgus alignment. No significant differences in PROMs were found between individual phenotypes or between preserved and altered phenotypes. CONCLUSION: Coronal alignment and joint line orientation were highly variable within a lateral compartment OA cohort. However, no association was demonstrated between superior postoperative PROMs and phenotype variation or phenotype preservation, which might suggest that there is not one universal optimal alignment target. Interestingly, 23.6% of knees with lateral compartment OA did not have a prearthritic valgus alignment, which may have been affected by joint line orientation.

Preservation of prearthritic coronal knee phenotype and prearthritic coronal alignment yielded improved Kujala scores following ligament-guided medial unicompartmental knee arthroplasty.

PURPOSE: There is a lack of literature evaluating outcomes of the ligament-guided approach in medial unicompartmental knee arthroplasty (UKA). An improved comprehension of the distribution of coronal plane alignment of the knee (CPAK) phenotypes and sagittal tibial wear patterns and their associations with patient-reported outcome measures (PROMs) and implant survivorship could provide insights into its further application in daily practice. METHODS: A registry was reviewed for patients with a minimal 2-year follow-up who underwent robotic-assisted, ligament-guided, medial UKA between 2008 and 2016. Survivorship and postoperative PROMs were collected. CPAK phenotypes and sagittal tibial wear patterns were determined. Survivorship, Knee Injury and Osteoarthritis Outcome Score (KOOS), Kujala and patient satisfaction were compared between phenotypes and sagittal tibial wear patterns. RESULTS: A total of 618 knees were included at a mean follow-up of 4.1 [2.0-9.6] years. Four-year conversion to the TKA survival rate was 98.9% [98.4%-99.3%] and 94.3% [93.3%-95.3%] for all-cause revision. Patients with preservation of the CPAK phenotype (84.5 ± 14.9, 81.8 ± 15.5, p = 0.033) and restoration of prearthritic coronal alignment (84.1 ± 14.9, 81.7 ± 15.9, p = 0.045) had a significantly higher Kujala score. No other significant differences in survivorship or PROMs were observed between phenotypes or sagittal tibial wear patterns. Additionally, no difference in survival rates was observed between preserved or altered phenotypes. CONCLUSION: This study demonstrated that preservation of CPAK phenotype and preservation of prearthritic coronal alignment yielded a significantly higher Kujala score. No other significant differences in PROMs or implant survivorship were observed, suggesting that robotic-assisted, ligament-guided medial UKA provides equal outcomes for all observed phenotypes and sagittal tibial wear patterns in medial compartment OA as long as preoperative CPAK phenotype is preserved postoperatively. LEVEL OF EVIDENCE: Level III.

Robotic-arm-assisted lateral unicompartmental knee arthroplasty leads to high implant survival and patient satisfaction at mean 10-year follow-up.

BACKGROUND: There is a lack of literature reporting on long-term outcomes following robotic-arm-assisted lateral unicompartmental knee arthroplasty (UKA). This study assessed the long-term survivorship, patient-reported satisfaction and pain scores following robotic-arm-assisted lateral UKA for lateral compartment osteoarthritis (OA). METHODS: A single surgeon's database was reviewed to identify all patients who underwent robotic-arm-assisted lateral UKA with a cemented, fixed-bearing prosthesis prior to May 2015. Patients were contacted to determine implant survivorship, satisfaction and pain. Kaplan-Meier models were applied to analyse survival. RESULTS: A total of 77 knees (70 patients) with a mean follow-up of 10.2 ± 1.5 years (range: 8.1-13.3) were included. Five knees were revised, corresponding to a 10-year survivorship of 96.1% and estimated survival time of 12.7 ± 0.3 years (95% confidence interval: 12.2-13.2) with all-cause revision as the endpoint. Unexplained pain (40.0%) and progression of OA (40.0%) in contralateral compartments were the most reported reasons for revision. Among patients without revision, 94.4% were either satisfied or very satisfied with their lateral UKA and the average pain score was 1.1. CONCLUSION: Robotic-arm-assisted lateral UKA led to high implant survivorship and patient satisfaction, and low pain scores at long-term follow-up. Progression of OA in contralateral compartments and unexplained pain were the most frequent reasons for revision. These findings support the continued use of robotic-arm-assisted lateral UKA for lateral compartment OA; however, its clinical value over conventional techniques remains to be established in prospective comparative studies. LEVEL OF EVIDENCE: Therapeutic Level IV.

The phenotypic diversity of anteromedial osteoarthritis before and after treatment with medial unicompartmental knee arthroplasty: A radiographic analysis of 1000 knees.

PURPOSE: This study aimed to assess phenotypic variation in the coronal plane of knees with anteromedial osteoarthritis using the functional knee phenotype classification, before and after treatment with medial unicompartmental knee arthroplasty (UKA). METHODS: The study comprised 1000 knees of 835 patients (45% females, 55% males, 90% Caucasian) who underwent medial UKA for anteromedial osteoarthritis. Pre and postoperative alignment was evaluated through the hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). Knees were classified according to the functional knee phenotype system which combines limb phenotype (HKA), and femoral and tibial knee phenotypes (FMA and TMA, respectively). Restoration of prearthritic coronal alignment following medial UKA was evaluated by phenotype. RESULTS: Preoperatively, 76 distinct and 25 relevant (prevalence ≥1%) functional knee phenotypes were identified, of which VARHKA 6°VARFMA 3°NEUTMA 0° was the most common (9.4% of knees). The most prevalent limb phenotype, VARHKA 6°, comprised 15 distinct knee phenotypes (FMA and TMA combinations). Postoperatively, 58 distinct and 17 relevant functional knee phenotypes were observed, of which VARHKA 3°NEUFMA 0°NEUTMA 0° had the highest prevalence at 18.3%. Knees with combined tibial and femoral deformities were associated with a lower probability of restoration of prearthritic coronal alignment following medial UKA, compared to knees without extra-articular deformity, or knees with an isolated tibial or femoral deformity. CONCLUSION: Phenotype analysis using the functional knee phenotype system demonstrated a wide diversity of coronal alignment phenotypes among knees with anteromedial osteoarthritis in a predominantly Caucasian population. Following medial UKA, a reduction from 25 preoperative to 17 postoperative relevant phenotypes was observed. Consideration of phenotypic variation can be of importance when aiming to restore prearthritic coronal alignment during medial UKA. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

Risk factors for intracellular fatty accumulation in rotator cuff muscle: a histologic analysis.

BACKGROUND: Fatty accumulation in rotator cuff muscles has been associated with shoulder dysfunction, risk of repair failure, and poor postoperative outcomes. This study sought to assess risk factors associated with true fatty accumulation based on histologic analysis and determine whether preoperative function directly correlated with this fatty rotator cuff accumulation. METHODS: Supraspinatus muscle biopsy specimens obtained prospectively from patients undergoing arthroscopic rotator cuff repair were stained with LipidTOX to quantify lipid accumulation. Two-step cluster analysis with Goutallier classification was used to define the fatty and non-fatty rotator cuff groups. We further performed a receiver operating characteristic curve analysis to confirm the group cutoff values. RESULTS: In total, 51 patients (aged 60.1 ± 10.5 years) were included. There were 19 high-grade partial tears, 10 small tears, 7 medium tears, 10 large tears, and 5 massive tears. Both cluster and receiver operating characteristic curve analyses yielded a cutoff value of 30% LipidTOX/4',6-diamidino-2-phenylindole (DAPI) separating the fatty vs. non-fatty groups. In the univariate analysis, patients with fatty rotator cuffs were aged 63.2 years on average compared with 59.7 years in the non-fatty group (P = .038). Female patients made up 57.1% of the fatty cohort, which was statistically higher than the non-fatty group (P = .042). Massive and large tears were more likely to occur in the fatty group (P = .005). In the multivariate analysis, full tendon tears had the largest predictive status of falling into the fatty group (odds ratio, 15.4; P = .008), followed by female sex (odds ratio, 4.9; P = .036). Patients in the fatty group had significantly higher American Shoulder and Elbow Surgeons scores (P = .048) and lower visual analog scale scores (P = .002). DISCUSSION AND CONCLUSION: This prospective histologic assessment revealed that full-thickness rotator cuff tears and female sex were the largest risk factors for intracellular lipid accumulation. Although tear size correlated with fatty accumulation, the sex disparity is a noteworthy finding that warrants further research.

Magnitude of Change in Leg Length and Clinical Impact Following Medial Unicompartmental Knee Arthroplasty.

BACKGROUND: Change in leg length and leg-length discrepancy (LLD) are common concerns among patients undergoing medial unicompartmental knee arthroplasty (UKA). This study aimed to quantify the magnitude of leg-length change, prevalence of postoperative LLD, and their clinical implications following medial UKA. METHODS: Leg length and mechanical hip-knee-ankle angle (mHKA) were retrospectively measured in 332 patients following unilateral robotic-arm assisted medial UKA for medial compartment osteoarthritis, using calibrated long-leg radiographs. The Knee Injury and Osteoarthritis Otcome Score for Joint Replacement and patient satisfaction were analyzed to assess impact of leg-length change and LLD on outcomes. RESULTS: Following medial UKA, median leg-length change was 2.0 mm (interquartile range, -1.0 to 5.0 mm; P < .001) with a mean correction in mHKA of 4.4° ± 2.7 (P < .001). A total of 158 patients (48%) had a leg-length increase by 0 to 5 mm, 64 (19%) by 6 to 10 mm, and 11 (3%) by >10 mm. Leg-length change was positively correlated with mHKA correction (R = 0.44, P < .001). Postoperatively, moderate (5 to 10 mm) and substantial LLD (≥10 mm) were present in 49% and 17% of patients, respectively. Four-year Knee Injury and Osteoarthritis Outcome Score for Joint Replacement were comparable between patients with and without substantial postoperative LLD (P = .976). Proportions of satisfied patients were similar between groups (P = .687). CONCLUSION: Following medial UKA, the majority of patients had a moderate increase in leg length, the magnitude of which was positively correlated to the correction in mechanical alignment. Postoperative substantial LLD was not uncommon (17% prevalence); however, it had no significant impact on patient-reported outcomes or satisfaction at 4 years follow-up.

Association Between Supraspinatus Tendon Retraction, Histologic Myofiber Size, and Supraspinatus Muscle Atrophy on MRI.

BACKGROUND: Atrophy of the rotator cuff is a negative prognostic indicator after rotator cuff repair. Although full-thickness rotator cuff tears accompanied by tendon retraction are commonly associated with decreased muscle cross-sectional area (CSA) on magnetic resonance imaging (MRI), it is unclear whether this is accompanied by histologic atrophy of rotator cuff myofibers. PURPOSE: To evaluate the effect of supraspinatus tendon retraction and myofiber size on supraspinatus atrophy on MRI. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Supraspinatus muscle biopsy specimens were obtained from consecutive patients undergoing arthroscopic shoulder surgery. Rotator cuff tears were classified according to size. Preoperative MRI was used to measure tendon retraction and CSA of the supraspinatus muscle in the Y-shaped view. The occupation ratio of the supraspinatus was calculated by dividing the supraspinatus CSA by the supraspinatus fossa CSA. Muscle biopsy specimens were examined using laminin to quantify myofiber CSA. The association between supraspinatus tear size and measures of histologic and MRI muscle atrophy were compared using standard statistical tests. Multivariable logistic regression analysis was used to identify independent predictors of muscle atrophy on MRI. RESULTS: A total of 38 patients were included: 8 with no tear, 14 with a partial-thickness tear, and 16 with a full-thickness tear. Increasing tear size was associated with greater distance of tendon retraction (P < .001), smaller mean histologic myofiber size (P = .004), lower mean supraspinatus CSA on MRI (P < .001), and lower occupation ratio: 0.73 (control), 0.66 (partial tear), 0.53 (small to medium full-thickness tear), and 0.38 (large to massive full-thickness) (P < .001). On Pearson correlation analysis, tendon retraction demonstrated strong correlation with occupation ratio (-0.725; P < .001) and weak correlation with myofiber size (-0.437; P = .006), while occupation ratio showed moderate correlation with myofiber size (0.593; P < .001). Multivariable linear regression analysis demonstrated that increasing tendon retraction (P < .001), age (P = .034), and smaller histologic myofiber CSA (P = .047) were independently associated with greater supraspinatus atrophy on MRI. CONCLUSION: Supraspinatus muscle atrophy appreciated on MRI is independently associated with patient age, tendon retraction, and atrophy of the supraspinatus myofibers at the histologic level.

Restoration or relative overcorrection of pre-arthritic coronal alignment leads to improved results following medial unicompartmental knee arthroplasty.

PURPOSE: A pre-arthritic alignment strategy for medial unicompartmental knee arthroplasty (UKA) aims to restore a patient's native lower limb alignment which may translate into improved outcomes. This study aimed to assess whether patients with pre-arthritically aligned knees versus patients with non-pre-arthritically aligned knees demonstrated improved mid-term outcomes and survivorship following medial UKA. The hypothesis was that pre-arthritic alignment in medial UKA would lead to better postoperative outcomes. METHODS: A retrospective study of 537 robotic-assisted fixed-bearing medial UKA was conducted. During this procedure, the surgical goal was to restore pre-arthritic alignment guided by re-tensioning of the medial collateral ligament (MCL). For study purposes, coronal alignment was retrospectively evaluated using the mechanical hip-knee-ankle angle (mHKA). Pre-arthritic alignment was estimated through the arithmetic hip-knee-ankle (aHKA) algorithm. Knees were grouped according to the difference between postoperative mHKA and estimated pre-arthritic alignment (i.e., mHKA - aHKA) as Group 1 (pre-arthritically aligned: mHKA restored within 2.0° of the aHKA), Group 2 (mHKA > 2.0° overcorrected relative to the aHKA), or Group 3 (mHKA > 2.0° undercorrected relative to the aHKA). Outcomes included the Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR), Kujala, proportions of knees achieving the patient acceptable symptom state (PASS) for these scores, and survivorship. PASS thresholds for KOOS, JR and Kujala were determined using a receiver operating characteristic curve method. RESULTS: A total of 369 knees were categorized as Group 1, 107 as Group 2, and 61 as Group 3. At 4.4 ± 1.6 years follow-up, mean KOOS, JR was comparable among groups, while Kujala was significantly worse in Group 3. The proportion of knees achieving the PASS for Kujala (76.5 points) was lower in Group 3 (n = 32; 59%) compared to Group 1 (n = 260; 74%) (p = 0.02). 5-year survivorship was higher in Group 1 and Group 2 (99% and 100%, respectively) compared to Group 3 (91%) (p = 0.04). CONCLUSION: Pre-arthritically aligned knees and knees with relative overcorrection from their pre-arthritic alignment following medial UKA demonstrated improved mid-term outcomes and survivorship compared to knees with relative under correction from their pre-arthritic alignment. These results encourage restoring or relatively overcorrecting pre-arthritic alignment to optimize outcomes following medial UKA, and caution against under correction from the pre-arthritic alignment. LEVEL OF EVIDENCE: IV, case series.

Robotic-assisted medial unicompartmental knee arthroplasty restores estimated pre-arthritic coronal limb alignment: A retrospective cohort study.

BACKGROUND: Robotic-assisted medial unicompartmental knee arthroplasty (UKA) aims to restore pre-arthritic (constitutional) limb alignment, by re-tensioning of the medial collateral ligament (MCL). This study aimed to determine whether pre-arthritic coronal alignment was restored following robotic-assisted medial UKA in patients with medial compartment osteoarthritis. METHOD: A retrospective study was undertaken, including 102 patients with a unilateral robotic-assisted medial UKA and a contralateral unaffected knee. Both the validated arithmetic hip-knee-ankle angle (aHKA) and alignment of the contralateral unaffected knee were used to estimate pre-arthritic alignment. The aHKA is a radiographic method to estimate the pre-arthritic mechanical hip-knee-ankle angle (mHKA). To verify restoration of pre-arthritic alignment, postoperative mHKA was compared to the aHKA. Additionally, postoperative mHKA, joint line congruence (JLCA), and knee joint line obliquity (KJLO) angles were compared between the operative and contralateral unaffected knee. Equivalence between postoperative and pre-arthritic alignment was assessed through the two-one-sided t-test (TOST), using equivalence margins of ±2.0°. RESULTS: Postoperative mHKA was equivalent to the aHKA (mean difference -0.38°, 90% CI -0.69 to -0.07;p < .001), with 93 knees (91%) restored within 3.0° of their aHKA. Postoperative mHKA, JLCA and KJLO were equivalent between the operative and contralateral unaffected knees, with mean differences of -0.65°, -0.65°, and -0.40°, respectively; all p < .001. CONCLUSIONS: Postoperative and pre-arthritic coronal alignment were equivalent following robotic-assisted medial UKA, with 91% of knees restored within 3.0° of their pre-arthritic mechanical axis. These results demonstrate that both mechanical alignment and joint line congruence are restored by MCL re-tensioning in patients undergoing robotic-assisted medial UKA for medial compartment osteoarthritis.

Successful same-day discharge in 88% of patients after unicompartmental knee arthroplasty: a systematic review and meta-analysis.

PURPOSE: The purpose of this study was to evaluate the effectiveness of day-case unicompartmental knee arthroplasty (UKA) by assessment of successful same-day discharge (SDD), readmission, complication and reoperation rates in the recent literature. METHODS: For this systematic review and meta-analysis, PubMed, Embase and Cochrane Library were comprehensively searched to identify all eligible studies reporting outcomes of day-case UKA. Studies with intended same-day home discharge after UKA were included. A meta-analysis of proportions, using a random-effects model, was performed to estimate overall rates of successful SDD and adverse events. Subgroup analyses were performed for studies including selected patients (i.e., patients had to meet certain patient-specific criteria to be eligible for day-case UKA) and unselected patients (i.e., no additional criteria for day-case UKA), as well as for clinical and registry-based studies. Additional outcomes included reasons for the failure of SDD and patient satisfaction. RESULTS: A total of 29 studies and 9694 patients were included with a mean age of 66 ± 9 years and mean follow-up of 59 days (mean range 30-270 days). Based on 24 studies (2733 patients), the overall successful SDD rate was 88% (95% confidence interval [CI] 80-92). These rates were 91% (95% CI 84-95) across studies with selected patients and 76% (95% CI 55-89) across studies with unselected patients. Overall readmission, complication and reoperation rates were 3% (95% CI 1.9-4.4), 4% (95% CI 2.8-5.2) and 1% (95% CI 0.8-1.3), respectively. Inability to mobilize, nausea and uncontrolled pain were frequently reported reasons for failed SDD. The overall patient satisfaction rate was 94%. CONCLUSION: This systematic review with meta-analysis found an overall successful SDD rate of 88% after UKA in a heterogeneous cohort of selected and unselected patients. Readmission, complication and reoperation rates suggest UKA can be performed safely and effectively as a same-day discharge procedure. LEVEL OF EVIDENCE: Level IV, systematic review of level III and IV studies.

Histologic Differences in Human Rotator Cuff Muscle Based on Tear Characteristics.

BACKGROUND: Fatty accumulation in the rotator cuff is associated with shoulder dysfunction and a risk of failure of rotator cuff repair. The aims of this study were to (1) describe cellular findings in rotator cuff muscles in patients presenting with varying degrees of rotator cuff tendon pathology by examining fat content and myofiber cross-sectional area of rotator cuff muscles and (2) correlate histologic features to magnetic resonance imaging (MRI) grades derived with the Goutallier classification. METHODS: Rotator cuff muscle biopsies were performed in a consecutive series of patients undergoing arthroscopic shoulder surgery. Rotator cuffs were graded according to the Goutallier classification and labeled as either partial-thickness or full-thickness. Patients without a rotator cuff tear undergoing arthroscopic surgery served as controls. The biopsy specimens were examined using LipidTOX to visualize lipid accumulation. Laminin was used to quantify myofiber cross-sectional area. RESULTS: Twenty-seven patients with a rotator cuff tear and 12 without a tear (controls) were included. There were 24 males (62%). The mean age was 55 years. Patients in the control cohort were younger (mean, 46 years) than those in the treatment group (mean, 60 years, p < 0.01). Within the treatment group, 12 and 15 patients were recorded as having partial and full-thickness rotator cuff tears, respectively. Lipid accumulation visualized at the cellular level was fairly-to-moderately correlated with the Goutallier classification on MRI (R s = 0.705, 95% confidence interval [CI] = 0.513, 0.829). Muscle biopsy specimens with a Goutallier grade of 2+ had significantly more lipid accumulation than those with grade-0 (p < 0.01) or grade-1 (p < 0.01) fatty accumulation. Muscle biopsies at the sites of full-thickness tears showed significantly greater lipid accumulation than those associated with either partial (p < 0.01) or no (p < 0.01) tears. Partial-thickness rotator cuff tears had no difference in lipid accumulation in comparison to the control group. Muscle biopsy specimens from full-thickness tears had significantly smaller myofiber cross-sectional area when compared with partial-thickness tears (p = 0.02) and controls (p < 0.01). CONCLUSIONS: Cellular lipid accumulation correlates with the MRI Goutallier grade of fatty accumulation, thus verifying the Goutallier classification at the cellular level. Muscle biopsy specimens from partial-thickness tears are more similar to controls than to those from full-thickness tears, whereas full-thickness tears of all sizes showed significantly greater lipid content and smaller myofiber cross-sectional area compared with partial-thickness tears and controls. CLINICAL RELEVANCE: Our research confirms the utility of using the Goutallier classification to predict rotator cuff muscle quality and shows that tendon attachment, even if partially torn, protects the muscle from fatty accumulation.