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Introduction Patellar fractures are rare at 1% incidence of all fractures. However, they can cause significant functional impairments due to the patella’s role in knee joint extension. Current scoring systems lack objectivity in assessing patellar healing. This study aims to validate the Radiographic Union Score for Tibia (RUST) using biplanar radiographs for assessing surgically treated patellar fractures. Materials and methods A retrospective analysis of radiological follow-up examinations was conducted on patients undergoing surgical treatment for patellar fractures from January 1st 2013, to June 30th 2023. Thirty patients were randomly selected, yielding 105 postoperative X-rays representing various healing stages. The modified Radiographic Union Score for Tibia (RUST) was applied to these X-rays by three independent trauma surgeons. Radiological follow-up examinations were randomized, pseudonymized, and stored on a hospital server for blinded assessment by three raters. The modified RUST assessed continuity of patellar borders and cortexes, assigning scores based on cortical bridging. Interobserver and intraobserver reliability were evaluated using intraclass correlation coefficients (ICC), adhering to recommended sample size criteria and interpretation guidelines. Results The mean modified RUST was 9.1 ± 2.2 points, with scores ranging from 4 to 12 points. The interobserver intraclass correlation coefficient (ICC) was 0.88 (95% CI, 0.81–0.92) and the intraobserver ICC were 0.6 (95% CI, 0.65–0.84), 0.80 (95% CI, 0.71–0.87) and 0.98 (0.98–0.99) respectively, which indicated good to excellent agreement. Conclusions This study validated the Radiographic Union Score for Tibia (RUST) for evaluating bone healing in patellar fractures treated with osteosynthesis, demonstrating good intra- and interobserver reliability. The modified RUST can provide a standardized method for assessing healing in patellar fractures, benefiting both clinical practice and clinical trials.

ObjectiveThe aim of this radiological study was to compare several relevant modified and newly applied patella height indices (PHI) in navigated primary total knee arthroplasty (TKA) to determine intra- and interobserver reliability in order to give a recommendation for clinical application in measuring patella height (PH) in primary TKA.Materials and methodsA retrospective data analysis assessing different PHI (modified Insall-Salvati index (mISI), Caton-Deschamps index (mCDI), Blackburne-Peel index (mBPI), Plateau-Patella Angle (mPPA); Miura-Kawaramura index (MKI), Knee-Triangular index (KTI)) on lateral knee radiographs was performed by two blinded observers using the same software three months pre- and postoperatively. Concordance correlation coefficient and Pearson’s correlation respectively were determined for intra- and interobserver rating as well as a categorization according to Landis and Koch and Cohen.ResultsA total of 337/291 patients of a 5-year period could be analyzed pre-/postoperatively. Excellent postoperative interrater results according to the categorization of Landis and Koch were achieved for the mBPI (Pearson 0.98) > mPPA (0.90) > KTI (0.86), good results for the MKI (0.79) and the mCDI (0.69), and moderate results for the mISI (0.52) with a predominantly strong Cohen correlation in almost all cases. Preoperatively, the mBPI and the KTI were the best interrated PHI. No PH changes could be found postoperatively for the mISI, KTI, MKI, and mPPA.ConclusionThe mBPI, the mPPA, and the KTI can be recommended for PH assessment in TKA. The mPPA might be the easiest one to use in a daily clinical set-up.

Purpose The aim of the study was to perform a systematic review and best knowledge synthesis of the present literature concerning biomechanical risk factors for developing first-time and recurrent patella dislocation. Methods The study was performed as a systematic review following PRISMA guidelines. PubMed and EMBASE were systematically searched. Studies investigating participants with risk factors for first-time as well as recurrent patella dislocation were included. The records were screened, and data extracted independently by two researchers supervised by a third independent assessor. The study was registered in PROSPERO. Results A total of 6233 records were screened, and 50 studies met the inclusion criteria. The biomechanical risk factors: trochlear dysplasia, increased tibial tuberosity–trochlear groove distance (TT-TG), and patella alta were found to be statistically significantly associated with patella dislocation in several publications and were thus recognized as risk factors for patella dislocation. The soft-tissue stabilizers: longer and thinner MPFL ligament, increased number of type 2C and decreased number of type 1 muscle fibers, and joint laxity were found to be statistically significantly associated with patella dislocation in a few publications, but due to limited evidence, no conclusion was made on this matter. Conclusion There is strong evidence in the literature that abnormalities of bony stabilizers, trochlear dysplasia, increased TT–TG distance, and patella alta are risk factors for patella dislocation. There is less evidence that soft-tissue stabilizers are risk factors. The study emphasizes the importance of a thorough investigation of bony stabilizers in clinical decision-making. Level of evidence Level IV.

Purpose The purpose of this retrospective study was to investigate the efficacy and functional outcomes of utilizing a flexible separate vertical suture fixation technique in osteoporotic patients presenting with comminuted fractures of the inferior patellar pole. Methods A flexible separate vertical suture fixation by braided polyester was applied. Between January 2021 and December 2022, 19 patients diagnosed as comminuted inferior patella fracture with osteoporosis were retrospectively enrolled in this study. Results The mean operative time was 34.2 ± 3.2 minutes, bone union achieved in all cases at an average of 3.1 ± 0.5 months after surgery. At the last follow up, the mean ROM was 132.1 ± 2.9°, and the mean Bostman score was 29.1 ± 0.9. During follow up, no instances of wire cutting or internal fixation failure occurred among the patients, no instances of postoperative anterior knee pain or refracture of the inferior patellar pole were observed and no surgical removal of implants was performed for any of the patients. Conclusions The flexible separate vertical suture fixation by thread is an effective fixation method for comminuted inferior patella fracture, especially for those elderly patients with osteoporosis.

Background The cable pin system is an effective device for fixation of transverse patella fractures. However, whether this device provides superior results using a minimally invasive technique instead of conventional open surgery using the K wire tension band method is unclear. Questions/purposes We asked whether a minimally invasive technique would be associated with (1) increased operative time; (2) reduced postoperative pain; (3) faster recovery of ROM; (4) higher knee scores; and (5) reduced complications. Methods Forty patients with displaced transverse fractures of the patella participated in this prospective, randomized, controlled trial. Twenty of these patients underwent a minimally invasive technique and the others had conventional open surgery using K wires. Some data for six of the 20 patients who underwent the minimally invasive technique were published in an earlier prospective, observational trial. At postoperative intervals of 1, 3, 6, 12, and 24 months, pain was measured by VAS scores, active flexion and extension of the knee were measured in degrees by goniometry, and knee function was evaluated using the Böstman clinical grading scale. Results Operative time was longer in the minimally invasive surgery group (54.3 ± 9.8 minutes versus 48.5 ± 6.1 minutes). Pain scores were better (lower) in the minimally invasive surgery group at 1 and 3 months but not at 6 months. Early flexion, ultimate flexion, and knee scores from 3 to 24 months, likewise, were better in the minimally invasive surgery group. Complications mostly related to symptomatic hardware were less common in the minimally invasive surgery group. Conclusions The minimally invasive technique is superior to conventional open surgery using K wires in terms of less early postoperative pain, better mobility angles of the injured knee, higher functional score of the injured knee, and decreased incidence of complications. Level of Evidence Level I, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Abstract IntroductionMany patella height indices exist in the literature. There is no single universally accepted radiological assessment for measuring patella height. The aims of this study were to determine which of the commonly used indices can most reliably measure patella height and compare the findings on both plain X-ray and magnetic resonance imaging (MRI) of the knee.MethodsThis case-controlled study compared patients with recurrent patella instability (patella group) to a control group. Two observers measured six validated patella height indices on X-ray and MRI of both groups at two separate time periods. Between-group and within-group statistical analysis was undertaken of the data. The inter- and intra-observer reliability was assessed using the intraclass correlation coefficient (ICC) and the kappa measure of agreement (k).ResultsForty-four patients comprised the patella group and 50 patients the control group. There was a significant difference of most indices between the two groups (p < 0.05). There was a significant difference of most indices between the two imaging modalities (p < 0.05). The Insall-Salvati ratio had the greatest inter-observer reliability for both X-ray and MRI (ICC = 0.79 to 0.97; p < 0.001) (k = 0.50 to 1.00; p < 0.001).ConclusionPatella height indices significantly differ when measured on X-ray as compared to MRI. This may infer that a different set of normative values are required for each radiological modality, which we have proposed in this study. Overall, the Insall-Salvati ratio performed best and shows a high degree of intra- and inter-observer reliability on both X-ray and MRI.

Purpose Trochlear dysplasia is an independent risk factor for recurrent patellar instability with evidence demonstrating its presence in up to 85% of patients with patellar instability. Severe trochlear dysplasia can be treated with trochleoplasty to improve engagement of the patella in the trochlear groove and prevent future dislocations. The aim of this study was to determine the clinical outcome of Bereiter trochleoplasty in patients with recurrent patellar instability and severe trochlear dysplasia. Methods This was a retrospective case series of all trochleoplasties performed in our institution from 2008–2019. All clinical records and pre-operative MRI scans were reviewed to assess for trochlear dysplasia, tibial tuberosity to trochlear groove distance (TTTG) and patella height using patella trochlear index (PTI). Trochlear dysplasia was classified using Dejour classification. Incidence of re-dislocation, infection, arthrofibrosis, chondral necrosis and re-operation were recorded. All patients were invited to complete a post-operative visual analog score for pain (VAS-P) and Banff Patella Instability Instrument (BPII). Results Fifty-eight trochleoplasties were performed in fifty patients during this period. All trochleoplasties were combined with additional procedures. 93% had concomitant medial patellofemoral ligament (MPFL) reconstructions and 47% had tibial tuberosity transfer. The mean follow-up period was 36.8 months. The rate of dislocation and arthrofibrosis were 5% each. There were no chondral necrosis or nonunion. The mean post-operative BPII was 58.4 and VAS-P was 30.4. Conclusions Bereiter trochleoplasty, often combined with MPFL reconstruction and/or tibial tuberosity transfer results in low re-dislocation and complication rate. Level of evidence IV.

Purpose External rotation of femoral component in total knee arthroplasty (TKA) with reference to the posterior condyles is recommended in mechanical alignment (MA) to ensure optimum patella tracking. In kinematic knee alignment (KA) technique, femoral component is more internally rotated as the femoral resection is based on flexion–extension axis. This study aims to investigate the clinical and radiological outcomes of the patellofemoral joint in patients who underwent TKA using KA versus mechanical alignment. Methods A review of prospectively collected registry data of 378 consecutive cruciate retaining primary TKAs (P.F.C. ® Total Knee System, DePuy Synthes, Massachusetts, United States) was performed. Propensity scoring was performed matching patients who received KA TKA ( n  = 93) to MA TKA ( n  = 93). Oxford Knee Score (OKS), Knee Society Score (KSS), Short-Form 36 (SF-36), range of motion as well as radiographs assessing patella tilt were compared at 6 months and 2 years after surgery. All patients received the same implant and had their patella resurfaced. Results OKS, KSS, physical component of SF-36 and satisfaction rates were comparable at both 6 months and 2 years after surgery. There was moderate association between preoperative and postoperative patella tilt in KA TKA (Cramer’s V  = 0.260, p  < 0.05). Postoperatively, KA group had a greater number of patients with lateral patella tilt compared to the mechanical group (12 [12.9%] vs 1 [1.1%], p  < 0.001). Patella tilts, however, resolved two years after surgery. Conclusion The relative internal rotation of the femoral component in KA TKA results in greater incidence of lateral patella tilt postoperatively. Nevertheless, patella tilt resolution was noted at 2 years. Level of evidence Level III Evidence—Retrospective Cohort Study.

Background The infrapatellar fat pad is one of the structures that obscures exposure in minimally invasive total knee arthroplasty (MIS TKA). Most MIS TKA surgeons (and many surgeons who use other approaches as well) excise the fat pad for better exposure of the knee. There is still controversy about the result of fat pad excision on patella baja, pain, and function. Questions/purposes In the setting of a randomized controlled trial, we sought to determine whether infrapatellar fat pad excision during MIS TKA causes (1) patellar tendon shortening (as measured by patella baja); (2) increased anterior knee pain; (3) decreases in the Knee Society Score or functional subscore; or (4) more patella-related complications. Methods We randomized 90 patients undergoing MIS TKA at one institution into two groups. In one group, 45 patients underwent MIS TKA with complete infrapatellar fat pad excision and in the other group, 45 patients received MIS TKA without infrapatellar fat pad excision. The patella was selectively resurfaced in these patients; there was no difference between the groups in terms of the percentage of patients whose patellae were resurfaced. We measured patellar tendon shortening, knee flexion, anterior knee pain, Knee Society Score (KSS), functional subscore, and patellar complications at preoperative and postoperative periods of 6 weeks, 3 months, 6 months, and 1 year; complete followup data were available on 86% of patients (77 of 90) who were enrolled. Results At the final followup, no significant differences were observed in patellar tendon shortening, KSS, functional subscore, or knee flexion in either group. However, patients with their infrapatellar fat pad excised experienced more anterior knee pain (8.3% versus 0%; p = 0.03; 95% confidence interval, −0.007 to 0.174) at the end of the study. No patellar complications were found in either group. Conclusions Infrapatellar fat pad excision in MIS TKA resulted in an increasing small percentage of patients with anterior knee pain after surgery. Surgeons should keep the fat pad if excellent exposure can be achieved but resect it if needed to improve exposure during TKA. Level of Evidence Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Disorders of the patella are among the most prevalent knee injuries. While exercise therapy is widely accepted as an effective treatment strategy, the positive effects of conventional exercise therapy under the guidance of a physiotherapist may be offset by inherent limitations, such as difficulties in scheduling appointments or statutory policies restricting the number of training sessions. Home-based exercise interventions using digital health applications (DHAs) may help address some of these limitations. This study aimed to assess the efficacy of a 12-week exercise intervention using a web-based DHA for improving knee function and reducing pain in patients with disorders of the patella (International Classification of Diseases code M22). The outcomes of the DHA intervention group (IG) were compared to a control group (CG) that received conventional physiotherapy covered by statutory health insurance in Germany (SHI-PT). A total of 259 patients with diagnosed disorders of the patella were included in the trial and randomly allocated to IG DHA (n=136, 52.5%) and CG SHI-PT (n=123, 47.5%). Two primary end points were examined: \"knee function\" (Knee Injury and Osteoarthritis Outcome Score-Activities of Daily Living [KOOS ] subscale, range 0-100 points) and \"knee pain\" (visual analog scale [VAS], range 0-100 points). Participants were asked to complete 2 surveys: one before the first therapy session (PRE) and one after completing the treatment period of 12 weeks (POST). Training with the DHA resulted in a 4.5-fold greater improvement in \"knee function\" (PRE-POST differences in KOOS score; IG DHA: 15.7 points, 95% CI 13.7-17.6 vs CG SHI-PT: 3.5 points, 95% CI 1.5-5.5) and a 3.5-fold greater reduction in \"knee pain\" (PRE-POST differences in VAS pain score; IG DHA: -22.5 points, 95% CI -25.2 to -19.9 vs CG SHI-PT: -6.5 points, 95% CI -8.7 to -4.4) compared to SHI-PT. The improvements in IG DHA exceeded the limits of clinical relevance. The differences between the treatment groups (KOOS score -10.1 points, 95% CI -infinity to -8.0; VAS pain score 14.3 points 95% CI 11.7-infinity) were statistically significant (P<.001) for both end points in favor of IG DHA. No effect was found for age or sex. The reported use of pain medication decreased substantially in IG DHA, and showed almost no change in CG SHI-PT. Our findings indicated that the investigated DHA is superior to SHI-PT for treating disorders of the patella. Therefore, DHA has been approved by the German Federal Institute for Drugs and Medical Devices for treating disorders of the patella in persons of all sexes aged ≥12 years. German Clinical Trials Register (DRKS) DRKS00023454; https://drks.de/search/en/trial/DRKS00023454.