Major Shortening of the Patellar Tendon During Septic Two-Stage Knee Arthroplasty Revision Using Static Spacers.

BACKGROUND: Two-stage septic revision knee arthroplasty (TKA) often results in inferior functional outcome after reimplantation, which might be due to impairments of the extensor mechanism. The aim of the current study was to elucidate possible alterations in extensor mechanisms during septic two-stage revision of TKA treated with a static spacer. METHODS: This retrospective study included 87 patients (42 women, 45 men, age 64.5 ± 10.5; range, 29-85 years) undergoing septic two-stage TKA revision using a static spacer. The modified Insall Salvati ratio (mISR) was calculated via calibrated true lateral radiographs by two independent orthopedic surgeons before TKA explantation (G0), 6-8 days after TKA removal (G1), one day before TKA reimplantation (G2) and 6-8 days after TKA reimplantation (G3). Age, sex, body mass index (BMI), index C-reactive protein level, and number of previous surgeries were evaluated to identify the possible correlations. RESULTS: Overall, mISR significantly decreased within the first 6 days after index surgery from 1.71 ± 0.41 to 1.63 ± 0.41 (G0 versus G1, P < .001) and showed a further decline within the next 6 weeks to 1.54 ± 0.39 (G1 versus G2, P = .002). Conversely, mISR increased after reimplantation of TKA to 1.6 ± 0.43 (G3 versus G2, P = .08), though it did not regain preoperative baseline levels (G0 versus G3, P < .001). The subgroup with mISR decrease ≥10% experienced patellar tendon shortening of 16% between G0 and G1, 19% between G0 and G2 and up to 20% between G0 and G3. There were weak correlations concerning age (r = -0.240, P = .038), preoperative C-reactive protein level (r = 0.239, P = .04) and patellar tendon shortening. Intraclass correlation coefficient (ICC)was 0.88 concerning radiographic measurement. CONCLUSION: Septic two-stage TKA revision using static spacers leads to irreversible alterations of the extensor mechanism, specifically a major shortening of the patellar tendon, in one out of 3 patients. LEVEL OF EVIDENCE: II.

Reliability of a Caton-Deschamps-derived patella height index for knee arthroplasty.

PURPOSE: The original Caton-Deschamps index (oCDI) detects functional patella height. It cannot be used in knees with an implanted endoprosthesis. The "modified Caton-Deschamps index" (mCDI) for knee arthroplasty can miss pseudo-patella-infera (PPI), which is common after TKA. A derivate of the oCDI could be a simple analogue to the index published in 1982 using a modified tibial reference point at the anterior proximal point of the inlay, which can indirectly be located on the lateral knee radiograph. It was the aim of this study to determine the intra- and inter-rater agreement of a derived Caton-Deschamps index (dCDI) for knee arthroplasty. We hypothesized that the derived Caton-Deschamps index (dCDI) is a reliable radiological measure for patella height in knee arthroplasty. METHODS: Several patella height indices were measured by three independent raters in two passes. The second pass was performed after 6 weeks in random order. Intra- and inter-observer agreements were determined and analyzed using the intraclass correlation coefficient (ICC). For radiographic evaluation, digital lateral radiographs of 150 knees before and after primary TKA were used. RESULTS: We found high interrater reliability for all analyzed indices. We found the highest agreements for the ISI preop (ICC = 0.914) and postop (ICC = 0.920), respectively. We also found very good intra-rater reliability for the CDI (ICCpreop = 0.954), dCDI (ICCpostop = 0.945), ISI (ICCpreop = 0.960; ICCpostop=0.940) and BPI (ICCpreop = 0.969; ICCpostop = 0.955). Fourteen cases (9.3%) with insignificant PPI were found. CONCLUSION: The derived Caton-Deschamps index (dCDI) can easily be used in knee arthroplasty and demonstrated high intra- and interrater agreement, which was similar to other commonly used and established patella height indices.

Distal tibial tubercle osteotomy is superior to the proximal one for progression of patellofemoral osteoarthritis in medial opening wedge high tibial osteotomy.

PURPOSE: To investigate the effect of proximal tibial tubercle osteotomy (PTO) and distal tibial tubercle osteotomy (DTO) in medial opening wedge high tibial osteotomy on patellofemoral alignment, patellofemoral osteoarthritis and clinical outcomes. METHODS: PTO (n = 41) and DTO (n = 43) for the same surgical indications were included. Radiographic measurements of the Caton-Deschamps index, patellar tilt and shift, and arthroscopic cartilage evaluation at the patellofemoral joint were performed at osteotomy and plate removal. The Knee Society Score (KSS) was evaluated preoperatively and at the latest follow-up. RESULTS: The follow-up period was longer in the PTO group (33.7 months; range 23-40 years) than in the DTO group (22.2 months; range 18-29 months) (p < 0.0001), whereas the period from osteotomy to plate removal was not different between the groups. The Caton-Deschamps index of the DTO group was unchanged from 0.9 (range 0.7-1.2) to 0.9 (range 0.6-1.4), whereas that of the PTO group changed from 0.9 (0.7-1.2) to 0.7 (0.5-1.0) (p < 0.0001). There were fewer deteriorated cases of cartilage status in the trochlear groove in the DTO group (20.9%) than in the PTO group (56.1%, p < 0.05). There were more improved cases in the DTO group (23.3%) than in the PTO group (4.9%, p < 0.05). Postoperative KSS was better in the DTO group than in the PTO group (p < 0.05). CONCLUSION: DTO is associated not only with reduced deterioration but also with increased improvement of cartilage status in the trochlear groove and better KSS as compared with PTO. LEVEL OF EVIDENCE: IV.

Is Pseudo-Patella Baja Really a Serious Complication of Total Knee Arthroplasty?

BACKGROUND: The available evidence on pseudo-patella baja (PPB) is limited. The purpose of this study is to investigate prospectively the occurrence of PPB after primary total knee arthroplasty and its clinical consequences in a large series of patients with a minimum follow-up of 2 years. PPB was defined as a patella distally displaced in relationship to the femoral trochlea with absence of patellar tendon shortening (Grelsamer RP. J Arthroplasty 2002;17:66-69) due to elevation of the joint line. METHODS: This study is a prospective case series of 354 patients with a mean age of 71.7 (range 52-87) years. Clinical evaluation was performed by the Knee Society Scores (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Short-Form 12-item (SF12), and range of motion. Patellar height was assessed by the Insall-Salvati and Blackburne-Peel ratios. RESULTS: The mean follow-up was 3.6 (range 2.0-6.6) years. Postoperatively, 286 (80.7%) patients had a normal patellar height, 17 (4.8%) had true patella baja (TPB), and 51 (14.4%) had PPB. There were no significant differences between the 3 groups in mean KSS-function (P = .107), range of motion (P = .408), WOMAC-pain (P = .095), WOMAC-stiffness (P = .279), or SF12-mental (P = .363). Between normal and PPB groups, there were no significant differences in mean KSS-knee (P = .903), WOMAC-function (P = .294), or SF12-physical (P = .940). However, the TPB group had significantly lower mean KSS-knee (P = .031), WOMAC-function (P = .018), and SF12-physical (P = .005) as compared with either 2 other groups. CONCLUSION: PPB was a relatively common finding, but no significant differences in terms of clinical outcomes were found as compared to patients with postoperative normal patellar height. TPB was infrequent, but these patients had significantly worse clinical outcomes than those with PPB or normal patellar height.

How is patella height modified after total knee arthroplasty?

INTRODUCTION: Since the first measurement method of patella height in 1929 (Janssen), more than 16 methods have been described. Most of these measures are not suitable to measure patella height after total knee arthroplasty (TKA). One of us (JC) modified the original Caton Deschamps (oCD), index with a new relative index called modified Caton Deschamps (mCD) index, by using new landmarks. The purpose of this study was to determine how patella height is modified after TKA. MATERIAL AND METHOD: Sixty primary TKAs were consecutively prospectively enrolled. One type of implant was used (cementless postero-stabilized TKA, rotating plateau, cemented patella resurfacing). Patient's characteristics, functional and radiological outcomes were recorded pre-operatively and at one year follow-up. Pre-operative and post-operative outcomes were compared by paired t-test. Post-operative outcomes were compared between groups by one-way analysis of variance. RESULTS: Average difference between pre and post-operative mCD was 0.19 in this series. In 81.7% of cases, patella was lowered. Patients were classified in three groups according to patella height lowering. Between these three groups, no significant statistical differences (IKS score knee and function, range of motion) could be identified. DISCUSSION: In TKA, patella assessment in sagittal plane is as important as frontal or horizontal planes. True patella infera (TPI) is mostly due to patella tendon shortening measured by oCD. Pseudo patella infera (PPI) measured by mCD is mostly due to joint line elevation (over femoral cut with an over thickness of the tibial component). In this study a moderate patella lowering (minor than 15%) does not have a significant impact on the functional results (IKS, ROM) nevertheless in 80% patella is lowered. The next step will be to analyze precisely what factors are influencing this lowering and what prevention could be suggested in primary and revision TKA.

Treatment of patella baja by a modified Z-plasty.

PURPOSE: The purpose of this study was to evaluate the efficiency of a modified Z-plasty for patellar tendon lengthening for the treatment of patella baja. Rather than adapting only two tendon reins according to the conventional Z-plasty method, the modified Z-plasty provides four reins to enable multifold overlapping of the tendon tissue. METHODS: Between 2010 and 2012, a modified Z-plasty procedure was performed in four patients suffering from patella baja. Physical examinations and standardized scoring instruments served as the evaluation measures. RESULTS: The median preoperative CD ratio of 0.53 (range 0.43-0.62) was corrected to 1.03 (range 1-1.06) after a median follow-up of 34 months (range 23-41 months). The median preoperative flexion of 108° (range 80-135°) improved to 143° (range 110-145°) compared with the flexion of 145° (range 140-145°) of the unaffected knee. No patients showed any signs of extension lag. The median Lysholm score improved from 49 (range 22-80) to 91 (range 67-95), and the Tegner activity level improved from 2 (range 0-6) to 6 (range 2-6). The median VAS status for pain decreased from an average of 8.5 (range 4-10) to 1 (range 0-2). No complications were observed. CONCLUSION: The modified Z-plasty procedure is a valuable technique for the treatment of patella baja, especially if allografts are not available. This procedure allowed for early mobilization and achieved excellent clinical results. LEVEL OF EVIDENCE: IV.

Changes in patella tendon length over 5 years after different types of knee arthroplasty.

PURPOSE: Post-operative shortening of the patellar tendon resulting in an abnormally low-lying patella has been described previously, but the degree of change in patella tendon length over time and extent of its progression after different types of knee arthroplasties remains unknown. This study assesses the incidence of patella tendon length change following lateral unicompartmental knee arthroplasty (UKA), medial UKA, and total knee arthroplasty (TKA), and its impact on patient-reported outcome at 5 years post-surgery. METHODS: Immediate post-operative, 1- and 5-year radiographs were reviewed for 50 patients undergoing each operation (n = 150), with the Insall-Salvati ratio used as a measure of patella tendon length. Clinical outcome was assessed using the Oxford Knee Score (OKS). RESULTS: At 5-year follow-up, no significant change in patella tendon length was found following medial UKA (1.07-1.05), whilst a significant shortening was found after TKA (1.02-0.96), and a significant lengthening found after lateral UKA (1.02-1.05). For the UKA groups, no further change in tendon length was observed after the first year post-surgery, whereas the TKA group continued to shorten between years one and five. OKS was significantly better in the UKA groups as compared to TKA group. Change in patella tendon length within individual groups did not correlate with OKS at 5 years. CONCLUSION: Patella tendon length shortening is more prevalent in TKAs, whilst lengthening is more prevalent in lateral UKAs. Despite the vertical incision through the patella tendon, lateral UKAs do not cause increased tendon shortening at 5 years post-surgery. However, in the medium term, changes in patella tendon length do not affect patient-reported outcome. LEVEL OF EVIDENCE: Retrospective, comparative study, Level III.

Patellar height assessment in total knee arthroplasty: a new method.

INTRODUCTION: We described in 1981 a method to evaluate patellar height in normal and symptomatic knees on sagittal X-ray view. This index is a frequently used method, yet it is not suitable after a total knee arthroplasty (TKA). MATERIAL AND METHOD: The original method measures the distance between the distal margin of the articular surface of the patella (point A) and the anterosuperior angle of the tibial plateau (point T), then the length of the patellar articular surface (AP). The index is AT/AP ratio (normal values range from 0.8 to 1.2). After TKA, the T landmark is no longer available, so we must define a new T' landmark. This point is situated at the intersection between the line perpendicular to the tibial posterior cortex elevated at the tip of the fibular head and the tibial anterior cortex. This remarkable landmark can be identified before and after TKA, with a new relative index AT'/AP ratio. This modified method allows the comparison of patella height before and after TKA. RESULTS: We have used this modified index with the collaboration of several authors during the testing of different models of TKA, with an accurate reproducibility. Repeatability (usually called intra-observer reliability) was good, with intra-class correlation coefficients (ICCs) between 0.58 and 0.75 among the observers. Reproducibility (usually called inter-observer reliability) was also considered as good, with ICC ranging from 0.64 to 0.72. DISCUSSION: Patella height measurement has to be assessed with the original method (AT/AP) to detect patella infera that could influence the surgical approach. The correlation between original and modified indexes has to be assessed. The modification of patella height after TKA could be evaluated through the modified index and compared with functional results.

Relationship between patellar tendon shortening and in vitro kinematics in the ovine stifle joint.

Post-operative patellar tendon shortening induces a distal positioning of the patella in the femoral trochlear groove, which has been associated with pain and impeded mobility. An idealized in vitro model was used to examine the effects of shortening on patellar kinematics. The PT length was progressively reduced by up to 5 mm (1-mm instalments) using a device secured onto the tendon in n = 9 ovine stifles. In vitro 6 degrees-of-freedom motion data for the patellofemoral and tibiofemoral joints under conditions of passively induced flexion-extension was acquired electromagnetically. Patellar motion was analysed as a function of both tibial and patellar flexion angles relative to the femoral co-ordinate frame. Linear regression with contrasts was used to compare kinematic changes for each shortening level, with significance set at P<0.01. A mean maximum percentage length reduction of 8.2% was achieved. Patellar flexion was linearly correlated with tibial flexion angle in the intact joint, and this correlation persisted after tendon shortening (R = 0.977, P < 0.01). Patellar kinematics expressed as a function of tibial flexion angle were significantly altered by a mean length decrease of 8.2%, while flexion and proximo-distal shift patterns were significantly affected at lesser shortening levels of 3.1% and 4.7%, respectively. Patellar kinematics expressed as a function of patellar flexion angle remained unchanged. These results suggest that patellar motion within the trochlear groove in the ovine stifle joint follows a repeatable three-dimensional path and that patellar tendon shortening advances the position of the patella along this path, without significantly altering it.

Surgical Treatment of Iatrogenic Patella Baja.

PURPOSE OF REVIEW: Patella baja is characterized by a loss of patellar height and can develop as either an acute or chronic complication following a knee injury or surgical procedure. The purpose of this review is to describe the diagnosis and management of patella baja and highlight the senior author's surgical technique. RECENT FINDINGS: The pathogenesis of patella baja involves a complex interaction between quadriceps dysfunction, immobilization, and inflammation leading to infrapatellar scarring and adhesions. It is associated with fractures about the knee and can result as a complication of surgical procedures such as anterior cruciate ligament (ACL) reconstruction, particularly bone-patellar tedon-bone autografts, high tibial osteotomies (HTOs), tibial tubercle osteotomies (TTOs), and total knee arthroplasties (TKAs). Patients with patella baja can have limited knee range of motion, anterior knee pain, significant weakness with active knee extension, and an extensor lag. Surgical intervention is indicated in cases of symptomatic patella baja. Treatment strategies include tibial tubercle proximalization, patellar tendon lengthening, and patellar tendon reconstruction. Allografts and autografts can be utilized to augment tendon lengthening or reconstructive procedures. Various small case series have reported favorable outcomes for these procedures. The treatment of patella baja is challenging and little consensus exists on optimal management, as much of the literature is limited to small case series. The preferred surgical technique of the senior author involves an end-to-end patellar tendon lengthening with hamstring autograft augmentation.

Patellar tendon lengthening and augmentation with quadriceps tendon graft for treatment of severe patella infera.

BACKGROUND: Patella infera represents a permanent abnormally low position of the patella with three characteristics: distal position of the patella in the femoral trochlea, permanent shortening of the patellar tendon, and decreased distance between the inferior pole of the patella and the articular surface of the tibia. Several surgical techniques have been described to resolve this disabling condition with varying outcomes. HYPOTHESIS: Lengthening of the shortened patellar tendon with augmentation using a quadriceps tendon graft in combination with excessive intra-articular release improve knee function in patients presenting with severe and permanent patella infera. METHODS: Nine patients (four males, five females) with significant patella infera were treated between 2004 and 2020. The low position of the patella was documented using the Caton-Deschamps index. The Tegner Lysholm knee scoring scale and the Numerical Rating Scale (NRS) for pain were used as outcome measures before surgery and at follow up. Complete data were available in 100% of cases at 12 months follow up, and in 78% at final follow up. RESULTS: The average follow up was 4.2 years (range, 1-16 years). The Tegner Lysholm score improved from a mean preoperative score of 43.8 to a mean postoperative score of 80.5. The median NRS status decreased from an average of 6.7 (range, 5-8) to 2.3 (range, 1-7). The median preoperative flexion was 103.3° (range, 40-125°), rising to 126.6° (range, 40-145°). The median preoperative Caton-Deschamps ratio of 0.32 (range, 0-0.6) improved to 0.99 (range, 0.9-1.1) at final follow up. Two patients needed additional surgical treatment (arthroscopic scar tissue removal and proximalisation of the tibial tuberosity). CONCLUSION: Lengthening of a shortened patellar tendon with augmentation using a quadriceps tendon graft combined with excessive intra-articular release is an individually adapted surgical salvage procedure to treat permanent patella infera. It improves knee function and yields good to excellent results in most cases.

Evaluation of patella height in native knees and arthroplasty: an instructional review.

Total knee arthroplasty (TKA) is the gold standard for treating advanced knee osteoarthritis. Among the postoperative complications of TKA are true patella infera (TPI) and pseudo patella infera (PPI), which should be differentiated since TPI exhibits significantly worse clinical outcomes. Multiple radiological patella height indices (PHI) exist; some were modified or originally designed for knees with implanted endoprostheses. However, there is no consensus on measuring and comparing patella height. Due to the lack of established, simple, reliable, and reproducible concepts for assessing patella height for arthroplasty, measuring patella height and the change of patella height by or after TKA have been challenging tasks for clinicians and researchers. This is a review of the current literature on methods for measuring patella height, with special attention to the ability to differentiate between the TPI and PPI after TKA. All literature on the topic was retrieved, and references from relevant articles were investigated until the end of April 2022.

Distal tibial tubercle osteotomy can lessen change in patellar height post medial opening wedge high tibial osteotomy? A systematic review and meta-analysis.

OBJECTIVE: Medial opening wedge high tibial osteotomy (MOWHTO) is a mainstream surgical method for treating early medial compartment knee osteoarthritis. Undesirable sequelae such as patella infera may happen following tuberosity osteotomy. We conducted this systematic review and meta-analysis to compare the change in patellar position after proximal tibial tubercle osteotomy (PTO) versus distal tibial tubercle osteotomy (DTO) intervention. METHODS: The 11 studies were acquired from PubMed, Medline, Embase and Cochrane Library. The data were extracted by two of the coauthors independently and were analyzed by RevMan5.3. Mean differences, odds ratios and 95% confidence intervals were calculated. Cochrane Collaboration's Risk of Bias Tool and Newcastle-Ottawa Scale were used to assess risk of bias. RESULTS: Eleven observational studies were assessed. The methodological quality of the trials ranged from moderate to high. The pooled results of postoperative patellar height (Caton-Deschamps index and Blackburne-Peel index) and postoperative complications showed that the differences were statistically significant between PTO and DTO interventions. Patellar index ratios decreased significantly in the PTO groups, and 12 (9.2%) complications under DTO surgery and 2 (1.6%) complications under PTO surgery were reported. The differences of postoperative posterior tibial slope (angle) was not statistically significant, but postoperative posterior tibial slope of both groups increased. Sensitivity analysis proved the stability of the pooled results and the publication bias was not apparent. CONCLUSIONS: DTO in MOWHTO maintained the postoperative patellar height, and clinically, for patients with serious patellofemoral osteoarthritis, DTO can be preferred. Postoperative complications are easily preventable with caution. In view of the heterogeneity and small sample size, whether these conclusions are applicable should be further determined in future studies.

Patella-height analysis and correlation with clinical outcome after primary total knee arthroplasty.

BACKGROUND: It is the aim of this study to conceptualize a scheme for patellar-height analysis suitable for knees without and with implanted endoprosthesis. Furthermore, patellar-height and change of patellar-height by total-knee-arthroplasty (TKA) should be studied and correlated with clinical outcomes. We hypothesize that not only True-Patella-Infera (TPI) but also Pseudo-Patella-Infera (PPI) might be correlated with elevated anterior-knee-pain and reduced range-of-motion. METHODS: Several patellar-height indices were measured by three independent raters in two passes. Indices were analyzed and intra- and interobserver agreements were determined. For radiographic and clinical evaluation of 92 knee arthroplasties, the Insall-Salvati Index (ISI) and the Caton-Deschamps Index (CDI) were used to determine patellar-height and especially the amounts of TPI and PPI. Patellar-height was correlated with clinical outcome parameters: pain, ROM, Oxford Knee Score, Knee Society Score, Kujala Score, SF-36, Tegner and Lysholm. RESULTS: All used patellar-height indices demonstrated good intra- and interobserver agreement. Low preoperative ROM was correlated with low postoperative ROM after primary TKA. Postoperatively, 2.2% of the patients had a TPI and 9.8% had a PPI. Patella infera was not correlated with reduced subjective or objective clinical outcome parameters. CONCLUSIONS: Preoperative ROM is a good predictor of postoperative ROM after primary TKA. Patellar-height analysis can be sufficiently performed using the ISI and the CDI, respectively the derived CDI (dCDI) in cases with implanted endoprosthesis. As an alternative to the CDI/dCDI, the BPI/mBPI can be used. There seems to be a certain threshold of acceptable patellar-height reduction, in which clinical outcome is not deteriorated.

Combined Patellar Tendon lengthening and partial Extensor Mechanism Allograft reconstruction for the treatment of patella infera: A case report.

Patella infera is an uncommon but potentially crippling pathology of the knee, resulting in stiffness and anterior knee pain. Several surgical methods have been described for its treatment, but there remains no clear technique of choice. We present the case of a 63-year-old male with patella infera, affecting a native knee, following Complex Regional Pain Syndrome. This patient was treated with a combined technique of Patellar Tendon lengthening and partial Hourglass Extensor Mechanism Allograft reconstruction. The results were excellent at 24 months of follow-up. To our knowledge, this technique has not yet been published, and we present it as a promising treatment option in selected cases.

Does knee position during wound closure alter patella height following total knee arthroplasty?

BACKGROUND: Patella infera is a known complication of total knee arthroplasty, and the method of soft tissue closure is a possible contributing factor. The aim of our study was to evaluate the effect of knee position during surgical closure of capsule, subcutaneous tissue and skin on patella tendon length after total knee arthroplasty. METHODS: A three arm retrospective cohort study was conducted in a single institution over a 3-year period; 75 patients were divided, by surgeon preference, into three groups (Flexed, Extended and Hybrid) of 25 patients. All groups had standardized prosthesis, intraoperative and postoperative protocols, and differed in knee position at closure. Patellar tendon length was assessed radiologically using Insall Salvati ratio (ISR) and modified Insall Salvati ratio, with a 12-month follow-up. Intraclass correlation coefficients were used to assess intraobserver variability. RESULTS: There was a small but significant difference in preoperative to initial postoperative ISR change between Flexed and Extended groups (Extended group mean ISR change = -0.05; t = -2.31, P = 0.025, independent samples t-test), which was not sustained at 12 months. The incidence of patella infera was similar in Flexed and Extended groups at 12 months with only one case seen in the Hybrid group. CONCLUSION: Our study suggests that knee position during soft tissue closure does not have a sustained impact on patella tendon length after knee replacement. A small but statistically significant reduction in patella height was found in the Extended group initially after surgery but this effect was not sustained at 12 months.

Abnormal Patella Height Based on Insall-Salvati Ratio and its Correlation with Patellar Cartilage Lesions: An Extremity-Dedicated Low-Field Magnetic Resonance Imaging Analysis of 1703 Chinese Cases.

BACKGROUND AND AIMS: Diagnostic performance of patellar position for patellar cartilage lesions remains unclear. The aim of this study was to assess the abnormal patella height and its correlation with chondral lesions of the patellofemoral joint in China. MATERIAL AND METHODS: A total of 1703 consecutive patients who performed knee joint examination using an extremity-dedicated low-field magnetic resonance imaging were enrolled in this study. Patellar cartilage lesions were diagnosed based on the result of magnetic resonance imaging and clinical data. Patella height was defined as the ratio of patellar tendon length to patellar length according to Insall-Salvati index. Patella alta and infera were defined as tendon length/patellar length >1.2 and <0.8, respectively. RESULTS: The total prevalence of patellar cartilage lesions was 38.0%. The prevalence in females was significantly higher than that in males (46.4% vs 28.8%, p < 0.001). Age notably increased the incidence of patellar cartilage lesions (p < 0.001). Logistic regression analysis showed that tendon length/patellar length ratio was significantly correlated with patellar cartilage lesions (odds ratio = 6.380, p < 0.001). Furthermore, patients with cartilage lesions showed significantly higher rates of patella alta and infera (p < 0.001). In addition, receiver operating characteristic curve analysis demonstrated that abnormal patella height had statistical significance in diagnosing cartilage lesions (p < 0.001). However, the area under the curve (0.596; 95% confidence interval: 0.568-0.624) and sensitivity (47.0%) were relatively low, while the specificity was 72.2%. CONCLUSIONS: Patients with patellar cartilage lesions have an increased tendon length/patellar length ratio. The abnormal patella height is significantly correlated with chondral lesions and can be used as a potential diagnostic marker.

Treatment of patella infera by patellar tendon lengthening and augmentation with tibialis anterior tendon allograft.

Management of patella infera remains a difficult therapeutic endeavor. We report a case of a 21-year-old man, who had development of patella infera and knee flexion contracture after a patella fracture. Patella infera was treated by patellar tendon lengthening and augmentation with a tibialis anterior tendon allograft fixed with bioabsorbable cross-pins. The patient regained an anatomic patellar position and full range of motion at two years after surgery.

Patella Infera in an HIV Positive Patient Following Total Knee Arthroplasty.

A lowering of the patella after total knee arthroplasty is accompanied by pain and a restriction of the range of motion. With its etiology being unclear at present, a multifactorial genesis is under discussion. For the first time, we present a case report describing an HIV infection as a possible cause of patella infera.A 54-year-old HIV-positive woman developed patella infera (Insall-Salvati ratio 0.6) with a painful restriction of motion 18 months after implantation of a bicondylar surface prosthesis. By changing to a partially coupled endoprosthesis, distalization of the joint line and partial patellar resection, the patient was free of symptoms with a ROM of 0°/0°/110°.All risk factors known from the literature could be excluded in this case, so that the presence of an HIV infection has to be discussed as a possible cause.