Pseudo-patella baja after total knee arthroplasty

Influence of Changes in Patella Indices on Total Knee Replacement Surgery Outcomes

Summary

Total knee replacement is increasingly widely prescribed, not only for degenerative joint disease but also for other problems such as articular cartilage disease, misalignment due to causes other than degeneration, bone and joint cancer, and diseases that cause joint destruction. However, changes in knee joint biomechanics as well as complications of the patellofemoral joint after surgery lead to instability, joint pain, patellar rupture, and patellar tendon rupture. These are issues that challenge surgeons as well as make patients hesitant when considering knee replacement surgery. Understanding the changes in patella index that can occur after total knee replacement surgery will help surgeons carefully evaluate patients before surgery and calculate intraoperative techniques to minimize complications.

Methods

Fifty-eight patients with 62 knees were diagnosed with osteoarthritis and underwent total knee replacement surgery. All patients had clinical and radiographic evaluation of the knee joint before and after surgery.

Results

Patellar indexes did not change significantly after surgery compared to before surgery. Before surgery, 2 patients (3.23%) had true patella baja. After surgery, 7 patients (11.29%) had true patella baja and 3 patients (4.84%) had pseudo-patella baja. The average knee flexion amplitude after surgery was 103.11±15.440, with only 2 patients losing extension >50º. The average KS score after surgery was 83.69±9.98, significantly improved compared to before surgery 33.44±11.38. Similarly, KFS score after surgery was 81.01±8.84 compared to before surgery 37.05±8.08.

Conclusion

Changes in index of the patella before and after surgery affect the surgical results, the normal patella group has better results than the group with patella baja.

Incidence of patella baja and pseudopatella baja in aseptic revision total knee arthroplasty

INTRODUCTION

There are two variants regarding the low location of the patella in relation to the tibio-femoral joint line: patella baja (PB) and pseudo-patella baja (PPB). The purpose of this study is to investigate the incidence of PB and PPB in a cohort of patients that underwent revision total knee arthroplasty (rTKA) for aseptic reasons and describe any differences in each group's ROM.

METHODS

This retrospective study included 114 patients that underwent aseptic revision TKA surgery between 2017 and 2022. Patients were revised either for stiffness (Group 1) or aseptic loosening/instability (Group 2). The Insall-Salvati ratio (ISR) and Blackburne-Peel ratio (BPR) were used to evaluate the patellar position. ISR < 0.8 defined PB, while cases with ISR ≥ 0.8 and BPI < 0.54 were defined as PPB. ROM was measured and a subanalysis was conducted to investigate the progression of the values of ISR and BPR.

RESULTS

55 patients comprised Group 1, and 59 patients comprised Group 2. Overall, 13 cases (11.4%) had PB before rTKA and 24 (21%) had PB after rTKA. Cases with PPB were 13 (11.4%) before and 34 (29.9%) after rTKA. Group 1 patients presented with more PB before and after rTKA (12.8% vs 10.2% and 27.3% vs 15.2% respectively). However, after rTKA Group 1 patients presented with less PPB (20%) compared to Group 2 (39%) (p = 0.02). In Group 1, patients with PPB after rTKA had less ROM compared to those without PPB [83.2 (± 21.9) vs 102.1 (± 19.9) (p = 0.025)]. The subanalysis (69 patients) showed a statistically significant decrease in ISR before and after rTKA (p = 0.041), and from the native knee to post-rTKA (p = 0.001). There was a statistically significant decrease in BPR before and after rTKA (p = 0.001) and from the native knee to both pre- and post-rTKA (p < 001).

CONCLUSION

After undergoing rTKA, the incidences of both patella baja (PB) and pseudo-patella baja (PPB) increased. Stiffness in the knee was associated with a higher incidence of PB, while non-stiffness cases showed a significantly higher incidence of PPB. Patients with stiff knees and PPB after rTKA experienced a significant reduction in range of motion (ROM). Additionally, the study revealed a noteworthy decrease in ISR and BPR with each subsequent surgery. This information is crucial for healthcare providers, as it sheds light on potential risks and outcomes of rTKA, allowing for improved patient management and surgical decision-making.

LEVEL OF EVIDENCE

III.

Change in patellar height in medial and lateral unicompartmental knee arthroplasty: a clinical trial

INTRODUCTION

Evidence on patellar height changes following unicompartmental knee arthroplasty (UKA) is lacking. Therefore, this study compared the patella height in patients who underwent medial versus lateral UKA. Moreover, a subgroup analysis was conducted to investigate whether sex, age, and BMI of the patients exert an influence on the postoperative patellar height.

METHODS

Radiographs and hospital records of patients undergoing UKA were prospectively collected. Surgeries were performed by one author with long experience in UKA in a highly standardised fashion. The implants were fixed-bearing medial PPK (Zimmer Biomet, Warsaw, Indiana, USA) and fixed-bearing lateral ZUK (Lima Corporate, Udine, Italy). The patellar height was measured using the Insall-Salvati and Caton-Deschamps indices.

RESULTS

A total of 203 patients were included: 119 patients were included in the medial and 84 in the lateral UKA. The mean age of the patients was 68.9 ± 6.7 years, and the mean BMI was 28.1 ± 4.1 kg/m2. 54% (110 of 203 patients) were women. On admission, between-group comparability was found in age, BMI, sex, and length of the follow-up. No between-group and within-group difference was detected pre- and post-operatively in the Insall-Salvati and Caton-Deschamps indices in patients who have undergone medial versus lateral UKA. Concerning the subgroup analyses, no between-group and within-group difference was detected pre- and post-operatively in all comparisons according to sex, age, and BMI.

CONCLUSION

No difference was found in patella height in patients who have undergone medial compared to lateral UKA. Furthermore, there was no evidence of an association between patient characteristics (sex, age, BMI) and patella height between medial and lateral UKA.

Difference Between Screw Cement Filling and Adequate Osteotomy With Thick Liner for Primary Primary Total Knee Arthroplasty in Patients With Rand IIb Tibial Defects

BACKGROUND

The effectiveness of 2 treatment options, screw-cement fill, and adequate osteotomy with a thick liner, in treating patients with Rand IIb tibial defects (tibial plateau defects to a depth of 5 to 10 millimeters) in primary total knee arthroplasty (TKA) has not yet been demonstrated. Therefore, we performed a retrospective study to evaluate the differences between these 2 treatments.

METHODS

We retrospectively analyzed patients who underwent primary TKA for Rand IIb tibial plateau defects from 2015 to 2020 from a department database. Patients were categorized into the screw-cement and thick liner groups based on the different options used to repair tibial defects. We evaluated Knee Society Score, range of motion (ROM), Insall-Salvati index (ISI), and Forgotten Joint Score (FJS) in both groups. We also compared differences in prosthesis survival, stiffness, myasthenia, and joint clicking between the 2 groups at mean 2 years postoperatively (range, 2 to 2.3). A power analysis was performed on the number of cases in the cohort.

RESULTS

Postoperative femur-tibia mechanical axis (FTMA) correction was significantly higher in the screw-cement group than in the thick-liner group: 18.8 (±5.6°) versus 15.4 (±5.9°) (P < .01); At mean 2 years after surgery, the American Knee Society Functional Score improvement values were higher in the thick-liner group than in the screw-cement group: 36.3 (±12.4) versus 42.4 (±16.4) (P = .05). Postoperative ISI scores were 0.95 (±0.12) points in the screw-cement group and 0.89 (±0.13) points in the-thick liner group (P = .03). There were no statistically significant differences in the Knee Society Clinical Score, ROM, FJS, stiffness, myasthenia, joint clicking, and revision rate.

CONCLUSION

The results of this study showed no significant difference in clinical outcomes between the 2 reconstruction strategies of the screw cement fill technique and the adequate osteotomy and thick liner technique for Rand IIb tibial plateau defects. However, in patients who have FTMA deformities greater than 20° or in younger patients who need to preserve bone volume, we recommend the screw cement filling technique to ensure stable postoperative results and to prepare these patients for possible later surgery.

Infection and Instability Increasing the Risk of Patella Baja and Pseudo-Patella Baja after Revision Total Knee Arthroplasty

Background

Patella baja with patellar tendon shortening due to traumatic or ischemic injury is a widely known complication after primary total knee arthroplasty (TKA). Pseudo-patella baja may arise from the elevation of the joint line after excessive distal femoral resection. The maintenance of original patellar height is important in revision TKA because postoperative patella baja and pseudo-patella baja can cause inferior biomechanical and clinical results. We investigated the incidence and risk factors of patella baja and pseudo-patella baja after revision TKA.

Methods

We retrospectively reviewed data for 180 revision TKAs. Patella baja was defined as a truly low-lying patella with an Insall-Salvati ratio (ISR) of < 0.8 and a Blackburne-Peel ratio (BPR) of < 0.54. Pseudo-patella baja was defined as a relatively low-lying patella compared to the joint line within the normal range of ISR and with a BPR of < 0.54. Clinically, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and range of motion (ROM) were evaluated. Risk factors increasing the incidence of patella baja and pseudo-patella baja after revision TKA were evaluated using multiple regression analysis.

Results

Before revision TKA, 169 knees did not exhibit patella baja or pseudo-patella baja, while 9 knees showed patella baja and 2 knees exhibited pseudo-patella baja. At 2 years after revision TKAs, 25 knees (13.9%) showed patella baja and 23 knees (12.8%) exhibited pseudo-patella baja. Despite no differences in the postoperative WOMAC score between groups with and without patella baja and pseudo-patella baja, the postoperative ROM was significantly smaller in the group with patella baja (113.3°) or pseudo patella baja (110.5°) than in the normal group (122.0°). Infection as the cause of revision TKA increased the risk of patella baja (odds ratio, 10.958; p < 0.001), and instability increased the risk of pseudo-patella baja (odds ratio, 11.480; p < 0.001).

Conclusions

Infection and instability resulted in increases in the incidence of patella baja and pseudo-patella baja after revision TKA. Information about the risk factors of patella baja and pseudo-patella baja will help TKA surgeons plan the height of the patella after revision TKA and improve clinical outcomes.

Additional Distal Femoral Resection Minimally Improves Terminal Knee Extension: A Systematic Review and Meta-Regression Challenging the Dogma

Background

Additional distal femoral resection is a common technique to address a flexion contracture during primary total knee arthroplasty (TKA) but can lead to midflexion instability and patella baja. Prior reports regarding the magnitude of knee extension obtained with additional femoral resection have varied. This study sought to systematically review research describing the effect of femoral resection on knee extension and to perform meta-regression to estimate this relationship.

Methods

A systematic review was conducted using MEDLINE, PubMed, and Cochrane databases by combining the terms ("flexion contracture" OR "flexion deformity") AND ("knee arthroplasty" OR "knee replacement") to identify 481 abstracts. In total, 7 articles reporting change in knee extension after additional femoral resection or augmentation across 184 knees were included. The mean value for knee extension, its standard deviation, and the number of knees tested were recorded for each level. Meta-regression was performed using weighted mixed-effects linear regression.

Results

Meta-regression estimated that each 1mm resected from the joint line produced a 2.5° gain of extension (95% confidence interval, 1.7 to 3.2). Sensitivity analyses excluding outlying observations estimated each 1mm resected from the joint line produced a 2.0° gain of extension (95% confidence interval, 1.9 to 2.2).

Conclusions

Each millimeter of additional femoral resection is likely to produce only a 2° improvement in knee extension. Thus, an additional resection of 2 mm is likely to improve knee extension by less than 5°. Alternative techniques, including posterior capsular release and posterior osteophyte resection, should be considered in correcting a flexion contracture during TKA.

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.

Effectiveness of proximal tibial tubercle transfer in patients with patella baja after total knee arthroplasty

Purpose

Patella baja after total knee arthroplasty (TKA) is a common problem that is usually treated via proximal transfer of the tibial tubercle. As the long-term outcomes of this procedure are unclarified, this study aimed to investigate the changes in clinical function and radiographic patellar height during five years of follow-up.

Methods

Sixty patients with patella baja after TKA who underwent proximalisation of the tibial tubercle were followed up for a mean of 71 months (range 21–153 months). The pre- and postoperative range of motion (ROM) and clinical scores (Knee Society Score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)) were compared. The radiographic patellar height was measured with the Caton-Deschamps index (CDI), Blackburne-Peel ratio (BP), and modified Insall-Salvati index (MIS).

Results

Proximalisation of the tibial tubercle resulted in a significant improvement in the ROM from 80° to 88°. The KSS and WOMAC did not improve or even worsened after the intervention. The radiographic patellar height immediately after tibial tubercle transfer was not better than prior to the intervention (CDI 0.72 vs. 0.63, p = 0.72; BP 0.66 vs. 0.61, p = 0.72; MIS 1.59 vs. 1.55, p = 1.00) and further decreased significantly so that the mean final values were worse than the values in the native joint (CDI 0.59 vs. 0.78, p = 0.001; BP 0.58 vs. 0.74, p = 0.001; MIS 1.39 vs. 1.81, p < 0.001).

Conclusion

Proximalisation of the tibial tubercle in patients with patella baja after TKA does neither lead to significant improvements in the clinical outcome nor in the radiographic patellar height during long-term follow-up.

Level of evidence

III

Factors Affecting Squatting Ability in Total Knee Arthroplasty Using High Flexion Prosthesis

Purpose

Total knee arthroplasty (TKA) is widely used as a treatment for knee osteoarthritis. Few studies have analysed the factors affecting the squatting ability of patients after TKA. The purpose of this study was to comprehensively analyse the factors affecting squatting ability after TKA and to determine which ones are important.

Patients and Methods

Three hundred primary TKA cases with a minimum 3-year follow-up were retrospectively analysed. All patients received a conventional posterior-stabilized TKA implant and underwent a standard perioperative care pathway. The patients were divided into two groups according to the squatting position and knee flexion angle while weight-bearing (Group I – inability to squat group, Group II – ability to squat group). Demographic, operative, and clinical data were collected. Radiographic assessment included joint line elevation, patellar position, posterior condylar offset (PCO), etc. Statistical analysis of the effect of all the above factors on squatting ability was performed.

Results

The preoperative range of motion and joint line of Group I were 82.9±12.6 and 3.24±1.07, respectively, and those of Group II were 107±9.6 and 1.83±0.89 respectively. The univariate analysis showed that age, prosthesis size, preoperative ROM and joint line position were correlated with squatting ability. But in the final multivariate analysis, joint line position and preoperative ROM were independent influencing factors that affected squatting ability after TKA (p value < 0.01).

Conclusion

Preoperative ROM and joint line position were independent influencing factors affecting squatting ability after TKA. Patients should be counseled accordingly and be made to understand these factors. To ensure that patients can squat postoperatively, we should improve surgical techniques to control joint line elevation.

Comparison of tibial anatomical-mechanical axis angles and patellar positions between tibial plateau levelling osteotomy (TPLO) and modified cranial closing wedge osteotomy (AMA-based CCWO) for the treatment of cranial cruciate ligament disease in large dogs with tibial plateau slopes greater than 30° and clinically normal Labradors retrievers

Background

The objective of this study was to evaluate tibial anatomical-mechanical axis angles (AMA-angles) and proximodistal and craniocaudal patellar positions following tibial plateau levelling osteotomy (TPLO) and AMA-based modified cranial closing wedge osteotomy (CCWO) in large dogs with tibial plateau angle (TPA) > 30°, to compare these postoperative positions with those of a control group of healthy normal dogs, and to assess which procedure yields postoperative morphology of the tibiae and stifles that is most consistent with that of the unaffected group. This study also investigated whether the occurrence of patellar ligament thickening (PLT), which is commonly observed 2 months postoperatively after TPLO, is associated with misplacement of the osteotomy. A total of 120 dogs weighing more than 20 kg, 40 of which were control animals, were enrolled in this retrospective study. Stifles were radiographically evaluated preoperatively and postoperatively on the side with CCLR and on the healthy contralateral side and compared with clinically normal stifles. PLT was reassessed after 2 months.

Results

Significant decreases in median patellar height ratio were found after both procedures (TPLO 0.24 (0.05–0.8); CCWO 0.22 (0.05–0.4)). The postoperative craniocaudal patellar position and the median AMA angle differed significantly among the groups (P = 0.000) (TPLO 87.5% caudal to the AA and 3.12° (0.76–6.98°); CCWO 100% cranial to the AA and 0° (− 1.34–0.65°); control group 5% caudal to the AA and 0.99° (0–3.39°)).

At 8 weeks, PLT grade differed significantly in the two operated groups (P = 0.000) (TPLO 40% 0–2, 20% 2–4, 40% > 4; CCWO 98.8% 0).

Conclusions

TPLO and AMA-based CCWO are associated with significant decreases in patellar height; however, the PLT results 2 months postoperatively differed between the two groups; the decrease in patellar height and PLT were independent of osteotomy position in the TPLO group. Compared to TPLO, CCWO results in reduced postoperative AMA angles and craniocaudal patellar positions that more closely resemble those of unaffected dogs, suggesting that the CCWO procedure allows us to better correct the caudal bowing of the proximal tibia that is often associated with deficient stifles in large dogs with TPA > 30°.

Pseudo-patella baja after total knee arthroplasty: Radiological evaluation and clinical repercussion

BACKGROUND

Anterior knee pain is an important complication after total knee arthroplasty (TKA). One possible contributor is the elevation of the joint line, known as pseudo-patella baja (PPB). Limited research has been conducted regarding this condition impacting TKA management. This study aims to evaluate the incidence, identify possible related factors and assess PPB clinical repercussions.

METHODS

A total of 813 consecutive TKAs were retrospectively reviewed. Patients were submitted to the same surgical procedure and information regarding TKA characteristics was collected. Lateral postoperative knee radiographs were analyzed using the modified Insall-Salvati Ratio and the Blackburne-Peel Index. A clinical evaluation was conducted on 112 knees where the Oxford Knee and Kujala Scores were applied. Range of motion was evaluated, and knee pain was assessed using the numeric pain rating scale, in addition to analgesic consumption.

RESULTS

A cohort of 612 knees was analyzed, of which 64 knees developed PPB (10.5% incidence). Statistically significant differences were found for advance components sizes (femoral P = 0.026 and tibial P < 0.001), polyethylene thickness (P < 0.001) and patients' height (P = 0.022) with smaller implant sizes, greater insert thicknesses and lower height showing an association with PPB. The PPB group had a significantly lower median Kujala score (P = 0.011), higher frequency of flexion contracture and of anterior knee pain (P = 0.039).

CONCLUSION

PPB has a clinical relevance that should not be overlooked. Its prevention through the recreation of the natural position of the joint line and correct choice of implant sizes and polyethylene thickness is of major importance and should always be considered.

Patella baja after intramedullary nailing of tibial fractures, using an infrapatellar/transtendinous approach, predicts worse patient reported outcome

Purpose

After intramedullary nailing of tibial shaft fractures using an infrapatellar/transtendinous approach, several patients suffer anterior knee pain. We suspect that the approach is associated with soft tissue scars and the development of a postoperative patella baja. The goal of the study is to investigate whether the development of patella baja is associated with worse subjective outcomes.

Methods

We retrospectively analyzed all patients in our orthopedic trauma department between 2011 and 2020 who underwent tibial fracture fixation via intramedullary nailing via an infrapatellar/transtendinous approach. Pre- and postoperative lateral knee x-rays were evaluated by measurement of the Insall-Salvati Index, and nail tip position. All patients were asked to answer the self-assessment Kujala questionnaire and Lysholm questionnaire.

Results

We included 78 patients (age: 44 ± 18 years) with a minimum follow-up of 12 months. Mean follow up was 59 ± 25 months. We included 50 male and 28 female patients. Patella baja detected by Insall-Salvati Index could be observed in 8 (10.3%) patients. Patients with patella baja showed significant worse function measured by the Kujala score 54 ± 18 vs. 80 ± 14 (p < 0.01). Likewise, Lysholm score did show significant differences between both groups (60 ± 24 vs. 86 ± 11; p < 0.01). Nail tip position was not associated with worse subjective function.

Conclusions

Patella baja in patients after tibial intramedullary nailing via an infrapatellar/transtendinous approach, is associated with worse subjective function and increased pain.

[Extended access to revision knee replacement : Intraoperative possibilities for improved joint exposure in complex knee arthroplasty procedures]

In most cases, a standard access via a medial parapatellar arthrotomy with a carefully performed release technique is sufficient for a good exposure of the knee joint in the revision situation. Crucial steps are targeted scar removal, sufficient soft tissue release and recreation of the shifting layers. Tuberosity osteotomy is an effective option for extended exposure at the distal joint region, facilitating a patella replacement to correct abnormalities in the patellofemoral joint. Extended exposure to the proximal joint is possible with the rectus snip and the VY plasty technique. Due to the rather poor results, a quadriceps turndown should be seen more historically and should no longer be used. In extreme cases, a femoral peel or an osteotomy of the medial epicondyle can help achieve the reconstruction of a joint. The latter techniques are reserved for selected cases and always require a linked implant.

Extracellular vesicles as novel approaches for the treatment of osteoarthritis: a narrative review on potential mechanisms

Osteoarthritis (OA) is a progressive degeneration of articular cartilage with involvement of synovial membrane, and subchondral bone. Current treatment approaches have focused on controlling the OA symptoms, pain, and inflammation. Recently, cell-based therapies, including the application of stem cells such as mesenchymal stem cells (MSCs), have been introduced for restoration of the articular cartilage. Despite promising outcomes, there are some limitations in the application of MSCs for OA treatment. It has been demonstrated that the regenerative potential of stem cells is related to the production of paracrine factors. Extracellular vehicles (EVs), the main component of cell secretome, are membrane-bounded structures that deliver biologically active agents. The delivery of molecules (e.g., nucleic acids, proteins, and lipids) leads to cell-to-cell communication and the alteration of cell functions. In this review, general characteristics of EVs, as well as their potential mechanisms in the prevention and treatment of OA were considered. Based on in vitro and in vivo studies, EVs have shown to contribute to cartilage regeneration via suppression of degenerative factors and regulation of chondrocyte function in the synthesis of extracellular matrix components. Also, they inhibit the progression of OA or protect the cartilage from degradation via their impact on inflammatory cytokines. The different signaling pathways of EVs against the pathologic features of OA were summarized in this review. According to the results obtained from several investigations, more investigations should be design to prove the safety and effectiveness of EVs in the treatment and prevention of OA progression.

[Biomechanical research on effects of pseudo-patella baja on stress of patellofemoral joint after total knee arthroplasty]

Objective

To investigate biomechanical effects of pseudo-patella baja on stress of patellofemoral joint after total knee arthroplasty (TKA) by using finite element analysis (FEA).

Methods

A series of CT and MRI of the left knee joint of two healthy volunteers and three-dimensional (3D) scanned data of TKA prosthesis were taken, and the 3D models of knee before and after TKA were established. The finite element model of pseudo-patella baja, normal patella, and alta patella after TKA were constructed by Insall-Salvafi (IS) ratio and Blackburne-Peel (BP) ratio. The load was applied along the direction of quadriceps femoris. After testing the validity of the finite element model, the high contact stress of patellofemoral joint was measured on the von Mise stress nephogram of pseudo-patella baja, normal patella, and alta patella after TKA when the knee flexion was 30°, 60°, and 90°. The average contact area was calculated according to two volunteers' data.

Results

On the finite element model of the normal patella after TKA with knee flexion 30°, 475 N pressure was applied along the direction of quadriceps femoris. The contact stress of patellofemoral joint was (1.29±0.41) MPa, which was similar to the results reported previously. The finite element model was valid. The von Mise stress nephogram showed that the stress mainly focused on the medial patellofemoral articular surface during knee flexion, and the contact point gradually moved up with the knee flexion deepened. The stress on the medial and lateral patellofemoral articular surface increased with the knee flexion deepened but decreased with the increase of patellar height. The effects of patellar height and knee flexion on the high contact stress of patellofemoral joint were similar among the finite element models after TKA based on the data of two volunteers. The high contact stress of patellofemoral joint increased with the knee flexion deepened in the same patellar height models ( P<0.05), but decreased with the increase of patellar height in the same knee flexion models ( P<0.05). The high contact stress of patellofemoral joint of pseudo-patella baja model was significantly higher than normal and alta patella models ( P<0.05). The average contact area of patellofemoral joint of pseudo-patella baja was bigger than normal and alta patella models with the knee flexion deepened.

Conclusion

The pseudo-patella baja after TKA has an important effect on the biomechanics of patellofemoral joint. Reserving the joint line and avoiding the occurrence of pseudo-patella baja can decrease the risk of anterior knee pain, patellar arthritis, and other complications caused by the increasing of contact stress of patellofemoral joint.

Variables affecting patellar height in patients undergoing primary total knee replacement

BACKGROUND

Alteration of patellar height is commonly encountered in total knee arthroplasty (TKA), and failure to address patella baja can result in suboptimal functional outcomes. It may therefore be prudent to evaluate pre-operative patellar height (PPH) and to seek risk factors for patella baja.

METHODS

Two hundred eighty-five patients who underwent TKA were included. Patient's age, gender, body mass index (BMI), and history of prior arthroscopy were recorded. PPH was measured using plateau-patella angle (PPA) as well as the Blackburn-Peel (BP), Caton-Deschamps (CD), and Insall-Salvati (IS) ratios.

RESULTS

The average patients' age was 71 years with a mean BMI of 30.45. There were 191 female and 94 male patients. One-fourth of the cases had at least one prior knee arthroscopy. Multivariate linear regression analysis identified gender and BMI as variables significantly affecting the IS ratio (p: < 0.05). Gender also had a significant correlation with PPA. Male patients were likely to have lower PPA (p: < 0.03). Though increasing age had a positive correlation with patellar height, this was not statistically significant. History of prior arthroscopy had no significant effect on any of the four PPH measurements.

CONCLUSION

Lower patellar height is significantly correlated to male gender and high BMI. We suggest that obese male patients be screened for pre-operative patella baja. This can help in surgical planning and optimizing results in TKA.

A new method for evaluation of patellar height and the position of the joint line before and after total knee arthroplasty

Background

The measurement of patellar height and restoration of the natural position of the joint line are crucial to total knee arthroplasty (TKA). However, there remains a lack of consensus on an optimal measurement method to associate the patellar height with the joint line position. The objective of this study was to introduce a new method and validate the application in TKA both preoperatively and postoperatively.

Methods

Instead of taking marginal landmarks as the tibial references, the tibial shaft axis was used to construct the new measurement method, which comprises the axis-patella (AP), joint axis-patella (jAP) indices and joint line height (JLH). Patellar heights were measured using the Insall-Salvati (IS), modified Insall-Salvati (mIS), Blackburne-Peel (BP), Caton-Deschamps (CD) indices, and the new method in 175 knees both preoperatively and postoperatively. Intraclass correlation coefficients and Pearson’s correlation analyses were respectively used to evaluate the reliabilities and correlations.

Results

There were good correlations between the proposed method and the mIS, CD, and BP indices. High inter-observer reproducibility was found for AP (preoperative and postoperative 0.83), jAP (preoperative 0.82; postoperative 0.86) indices and JLH (preoperative 0.88; postoperative 0.95). High intra-observer repeatability was also found for AP (preoperative 0.85; postoperative 0.87), jAP (preoperative 0.83; postoperative 0.87) indices and JLH (preoperative 0.80; postoperative 0.92).

Conclusions

The new method is reliable for measuring patellar height before and after TKA, providing an alternative to distinguish between true and pseudo patella baja. Furthermore, JLH can be applied to assess and restore the joint line position in TKA.

Reduction of Patella-baja and Pseudo-patella-baja Does Not Improve Range of Motion in Patients After Mega-TKA

BACKGROUND/AIM

Patella baja (PB) and pseudo-patella baja (PPB) have been shown to negatively influence outcomes after total knee arthroplasty. We hypothesized that there is a high incidence of PB and PPB after megaprosthetic total knee arthroplasty (M-TKA), and that this is associated with reduced range of motion.

PATIENTS AND METHODS

We retrospectively analysed all patients in our Orthopaedic Trauma Department after distal femur or proximal tibia replacement. Preoperative and one-year postoperative follow-up included measurement of range of motion and detection of PB and PPB using radiological indices.

RESULTS

We included 44 patients (age: 73±19 years). Preoperative PB detected by ISI could be reduced from 13 (36%) to 11 (25%) (p<0.01). Preoperative vs. postoperative ISI was 0.88±0.23 vs. 1.06±0.45 (p=0.03). PPB was observed preoperatively in 23 (63%) patients vs. 24 (54%) postoperatively. Preoperative vs. postoperative CDI was 0.70±0.24 vs. 0.95±0.43 (p=0.002). Preoperative flexion was 91°±30° vs. 85°±24° postoperatively (p>0.05).

CONCLUSION

Both PB and PPB are frequently observed after M-TKA. A reduction in PB and PPB alone does not improve postoperative range of motion.

Kinematically aligned TKA restores physiological patellofemoral biomechanics in the sagittal plane during a deep knee bend

PURPOSE

Although patellofemoral complications after kinematically aligned (KA) TKA are infrequent, the patellar flexion angle and proximal-distal patellar contact location through flexion, and incidence of patellar loss of contact at full extension are unknown. The present study determined whether the patellar flexion angle and proximal-distal patellar contact location of a KA TKA performed with anatomic, fixed-bearing, posterior cruciate-retaining (PCR) components differed from those of the native contralateral knee during a deep knee bend, and determined the incidence of patellar loss of contact at full extension for KA TKA only.

METHODS

During a deep knee bend from full extension to maximum flexion, both knees were imaged in a lateral view using single-plane fluoroscopy for 25 patients with a calipered KA TKA and a healthy native knee in the contralateral limb. The patellar flexion angle and proximal-distal patellar contact location were measured on images from full extension to maximum flexion in 30° increments. Paired t tests at each flexion angle determined the significance of the difference between the KA TKA knees and the native contralateral knees. In the KA TKA knees, the incidence of patellar loss of contact at full extension was determined. Patient-reported outcome scores also were recorded including the Oxford Knee Score.

RESULTS

Mean patellar flexion angles were not different between the KA TKA knees and the native contralateral knees throughout the motion arc. The largest statistically significant difference in the mean proximal-distal patellar contact locations was 4 mm. The incidence of patellar loss of contact in the KA TKA knees at full extension was 8% (2 of 25 patients). The median Oxford Knee Score was 46 out of 48.

CONCLUSIONS

Calipered KA TKA performed with anatomic, fixed-bearing, PCR components restored patellar flexion angles to native and largely restored the proximal-distal patellar contact locations, which at most differed from the native contralateral knee by approximately 10% of the mean proximal-distal patellar length. In the KA TKA knees, the incidence of patellar loss of contact was infrequent. These objective biomechanical results are consistent with the relatively high subjective patient-reported outcome scores herein and support the low incidence of patellofemoral complications following KA TKA previously reported.

LEVEL OF EVIDENCE

Therapeutic, level III.

Patella Baja in Total Knee Arthroplasty

Patella baja in total knee arthroplasty can result in impingement, pain, and decreased range of motion. Etiology can range from previous knee surgeries such as anterior cruciate ligament reconstruction, retrograde femoral nail, infrapatellar fat pad resection, and previous total knee arthroplasty. Diagnosis can be confirmed by one of a number of measurements of patellar height including Insall-Salvati and Blackburne-Peel ratios. It is important to differentiate between true patella baja and pseudopatella baja by patellar height ratio. Treatment includes correct identification of the underlying etiology and appropriate management. Surgical management strategies include tibial tubercle osteotomy, distal femoral augment and revision, proximalization of the patellar component, modification of the anterior tibial component, and/or Z-plasty of the patellar tendon. We review the outcomes for each of these procedures.

Medial stabilizing technique preserves anatomical joint line and increases range of motion compared with the gap-balancing technique in navigated total knee arthroplasty

BACKGROUND

Medial compartment stability is important in total knee arthroplasty. The medial stabilizing technique (MST) has been proposed to achieve medial stability without excessive medial soft tissue release in total knee arthroplasty. Herein, we compare the MST and the gap-balancing technique (GBT) in navigated total knee arthroplasty.

METHODS

We retrospectively analyzed 70 patients with varus knee osteoarthritis who underwent primary total knee arthroplasty using the navigation system. They were divided into MST (n = 39) and GBT (n = 31) groups. We assessed intraoperative navigation data, radiographic data, and insert thickness. Preoperative and postoperative joint line changes were measured. We also assessed range of motion and clinical instability before and after total knee arthroplasty. These parameters were statistically compared between the groups.

RESULTS

Compared with the GBT group, medial extension gaps were significantly smaller in the MST group (P = 0.008). The gap difference between medial and lateral extension was significantly greater in the MST group (P = 0.018). Other navigation data showed no significant differences. Insert thickness and joint line changes were significantly lower in the MST group (P = 0.001, P = 0.018, respectively). Postoperative range of motion was significantly greater in the MST group (P = 0.032). There was no objective or subjective knee instability in either group.

CONCLUSION

The MST could avoid knee joint line changes and might increase postoperative range of motion. Although the MST permitted a discrepancy between medial and lateral gaps, no patients felt knee instability. The MST might improve the results of total knee arthroplasty.

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.

The Effect of Patellar Tendon Release on the Characteristics of Patellofemoral Joint Squat Movement: A Simulation Analysis

Objectives: This paper studies the patellar tendon release’s effect on the movement characteristics of the artificial patellofemoral joint squat to provide reference data for knee joint surgery. Methods: Firstly, the dynamic finite element model of the human knee joint under squatting was established. Secondly, in the above no-release models, the release of 30% of the attachment area at the upper end, the lower end, or both ends of the patellar tendon were conducted, respectively. Then the simulations of all above four models were conducted. Finally, the results of the simulation were compared and analyzed. Results: The simulation results show that, after releasing the patellar tendon (compared with the no-release simulation’s results), the relative flexion, medial-lateral rotation, medial-lateral tilt, and superior-inferior shift of the patella relative to the femur increased; the medial-lateral shift and anterior-posterior shift of the patella relative to the femur decreased. Conclusion: In this paper, the maximum flexion angle of the patella increased after the patellar tendon being released (compared with the no-release model), which indicated that the mobility of knee joint was improved after the patellar tendon release. The simulation data in this paper can provide technical reference for total knee arthroplasty.

Femoral joint line restoration is a major determinant of postoperative range of motion in revision total knee arthroplasty

PURPOSE

The purpose of this study was to comprehensively analyze the effects of femoral or tibial joint line elevation and patella height change on the clinical results after revision total knee arthroplasty (RTKA) and to determine which one is the significant factor that should be restored.

METHODS

One hundred and sixty-six RTKA cases (144 patients) with a minimum 2-year follow-up were retrospectively analyzed. Demographic, operative, and clinical data were collected. Tibial and femoral joint line elevations were measured based on the distance from the tibial tubercle and from the adductor tubercle to the distal end of the femoral component, respectively. The patellar position was evaluated using the Insall-Salvati ratio and Blackburne-Peel index. The effects of clinical and radiological variables on the changes of range of motion (ROM) and clinical scores after RTKA were analyzed.

RESULTS

Fourteen knees (8.4%) showed a femoral joint line elevation of more than 5 mm, and 79 knees (47.6%) showed a tibial joint line elevation of more than 5 mm. Patella baja after RTKA was observed in 33 knees (19.9%), and pseudo-patella baja after RTKA was observed in 90 knees (54.2%). The linear mixed model revealed that the femoral joint line position was the only significant factor that affected the change of ROM after RTKA. No statistically significant correlation was observed between variables and postoperative clinical scores.

CONCLUSIONS

Restoration of femoral joint line was the significant factor that increased postoperative ROM of the knee after RTKA. In complicated revision situations, surgeons should give priority to the restoration of distal femoral joint line to increase postoperative ROM.

LEVEL OF EVIDENCE

IV.

Blackburne-Peel ratio predicts patients' outcomes after total knee arthroplasty

PURPOSE

Alterations in patellar height and posterior tibial slope (PTS) are frequently measured radiographic parameters associated with postoperative impairments after total knee arthroplasty (TKA). Few studies correlate the clinical outcome of TKA with the radiological indices. Both the modified Insall-Salvati ratio (mISR) and the Blackburne-Peel ratio (BPR) were hypothesised to correlate with the clinical outcome after TKA.

METHODS

A total of 282 computer navigated primary LCS^®-TKAs, implanted in our institution from 2008 to 2012, were included. Data (ROM, FJS-12, WOMAC, and revision surgery) were collected independently and prospectively. Patellar height (mISR, BPR), joint-line position, and PTS were measured on pre- and postoperative radiographs. Bivariate and multiple regression analyses were performed.

RESULTS

Mean mISR (1.5-1.4) and BPR (0.8-0.6) decreased from preoperatively to 1 year follow-up. Mean joint-line shift in a cranial direction was 2 mm after TKA implantation. Analysis of dichotomous variables (presence of PB and PPB or not) only showed significantly lower flexion in patients with PPB (p < 0.001). However, multiple regression revealed that BPR was a significant positive independent predictor for FJS-12 (p = 0.016) and flexion (p < 0.001) at 1 year follow-up. Postoperative PTS (p < 0.01) and initial patella height (p < 0.001) were both predictive for BPR at follow-up, while the joint-line height was not.

CONCLUSIONS

The BPR is a useful and reliable radiographic parameter to predict patient outcomes 1 year after primary navigated TKA. Lowering the BPR should be avoided, as this may lead to significant restrictions in terms of ROM and PROMs.

LEVEL OF EVIDENCE

Level 3.

Influence of Patella Height on Total Knee Arthroplasty: Outcomes and Survival

BACKGROUND

The aim of this study is to assess clinical results of total knee arthroplasty (TKA) with pre-operative patella alta or patella baja, compared to TKA with pre-operative normal patellar height.

METHODS

Patella height was measured using the Blackburne-Peel (BP) method in an initial, prospective cohort of 4103 TKAs performed at a single center. Three groups were defined: normal patella height (0.54 < BP index ≤ 1.06), patella alta (BP index >1.06), and patella baja (BP index ≤0.54). Pre-operative and post-operative clinical and radiological characteristics were collected and compared. All prostheses used a system of posterior stabilization by a third condyle. The primary outcome measure was the post-operative Knee Society Score. Statistical analysis was performed using Student's t-test and chi-squared test, with P < .05.

RESULTS

Two hundred twenty-three TKAs with pre-operative patella alta, 307 TKAs with pre-operative patella baja, and 2248 with pre-operative normal patella height, mean follow-up 39.3 months (range 24-239), were ultimately included. Post-operatively, there was no difference between the 3 groups in terms of Knee Society Score (knee and function scores). Patella baja statistically decreased the maximal flexion (118.2° vs 115.5°, P = .002) and increased the rate of patellar fracture (0.9% vs 2%, P = .05). Finally, survival rates were similar in the 3 groups with each above 91% (±2%) at 10 years.

CONCLUSION

Clinical and radiological results for TKAs with pre-operative patella alta and patella baja were comparable to TKAs with a normal pre-operative patellar height. Risk of post-operative patellar fracture increased for patients with pre-operative patella baja.

Impact of intraoperative adjustment method for increased flexion gap on knee kinematics after posterior cruciate ligament-sacrificing total knee arthroplasty

BACKGROUND

In general, the flexion gap is larger than the extension gap with posterior cruciate ligament-sacrificing total knee arthroplasty. Several methods compensate for an excessive flexion gap, but their effects are unknown. The purpose of this study was to compare three methods to compensate for an increased flexion gap.

METHODS

In this study, squatting in knees with excessive (4 mm) and moderate (2 mm) flexion gaps was simulated in a computer model. Differences in knee kinematics and kinetics with joint line elevation, setting the femoral component in flexion, and using a larger femoral component as compensatory methods were investigated.

FINDINGS

The rotational kinematics during flexion with setting the femoral component in flexion were opposite to those in the other models. Using a larger femoral component resulted in the most physiological motion. The peak anterior translation was 10 mm in the joint line elevation model compared with approximately 6 mm in the other models. In the joint line elevation model, patellofemoral contact stress was excessively increased at 90° of knee flexion. In contrast, tibiofemoral contact stress was higher during knee extension with setting the femoral component in flexion due to anterior impingement. There were few differences in the effect of the three compensatory methods with a moderate flexion gap.

INTERPRETATION

A larger femoral component should be used to compensate for an excessive flexion gap because it has less negative impact on posterior cruciate ligament-sacrificing total knee arthroplasty, whereas any compensation method might be acceptable for a moderate flexion gap.

The negative effect of joint line elevation after total knee arthroplasty on outcome

PURPOSE

Total knee arthroplasty (TKA) is widely used as a treatment for knee osteoarthritis. However, still up to 20% of the patients are dissatisfied. Joint line elevation after TKA might be a contributing factor as it alters knee kinematics. The aim of this study was to investigate the effect of joint line elevation on outcome.

METHODS

A systematic review of the literature was performed to select studies that reported on joint line alterations after primary or revision TKA and outcome. Studies with comparable outcome parameters were included in a correlation analysis.

RESULTS

In total, 396 studies were identified, of which 27 met the inclusion criteria. 8 studies could be included in the correlation analysis. Mean joint line elevation after primary TKA was 3.0 mm and after revision TKA this was 3.6 mm. A statistically significant negative correlation was found between joint line elevation and the postoperative Knee Society Score (KSS) function score (ρ = - 0.496, p < 0.001). In a pooled analysis, the maintained joint line revision TKA group had statistically significant better postoperative KSS total scores compared to an elevated joint line group (p < 0.001).

CONCLUSION

In this systematic review, a negative correlation between joint line elevation and outcome was found. Furthermore, revision TKAs with a maintained joint line have statistically significant better postoperative KSS scores compared to an elevated joint line group. To achieve optimal outcome after TKA, restoration of the joint line is one of the parameters that should be pursued and introduced elevation should not exceed 4 mm.

LEVEL OF EVIDENCE

IV.

Pseudo-patella baja: a minor yet frequent complication of total knee arthroplasty

PURPOSE

One of the complications in total knee arthroplasty (TKA) is pseudo-patella baja (PPB). PPB is present when there is no shortening of the patellar tendon, but the joint line is elevated. The purpose of this study is to investigate the incidence of PPB after TKA and its clinical effects.

METHODS

A case series of 158 patients undergoing TKA surgery between 1999 and 2012 at the 2nd Department of Orthopaedics and Traumatology, Pisa were retrospectively reviewed. Surgeries were performed by three senior surgeons, using the same surgical procedure for the implantation of a cemented posterior stabilized prosthesis. Lateral radiographs at 30° knee flexion were evaluated and the presence of PPB defined as modified Blackburne-Peel Index (mBPI) of < 0.54. All the patients were clinically evaluated using the Knee Society Score (KSS) and the Western Ontario and McMaster Universities Osteoarthritis Index score (WOMAC). Anterior knee pain was evaluated by visual analogue scale (VAS) and range of motion (ROM) was assessed through clinical examination.

RESULTS

The cohort group consisted of 158 patients, 109 (69.0%) female and 49 (31.0%) male. Median age at time of surgery was 74 years (range 36-87) and median follow-up was 66 months (range 12-163 months). Bilateral TKA surgery was performed in 50 patients, resulting in a total of 208 implants for investigation. On radiological evaluation, 139 (66.8%) showed no abnormalities (no joint line elevation and no patellar tendon shortening) and 55 (26.4%) presented joint line elevation with absence of patellar tendon shortening (PPB). No significant differences were found between the groups in terms of the KSS, WOMAC score, VAS or ROM.

CONCLUSION

Post TKA PPB is a relatively common complication. Careful preoperative planning, adequate soft tissue release, optimal cutting of bone components, on the femoral side in particular, and the use of thin polyethylene inserts can help to avoid this complication.

LEVEL OF EVIDENCE

IV.

Application of different patella height indices in patients undergoing total knee arthroplasty

BACKGROUND

One complication of total knee arthroplasty (TKA) is patella baja (PB). Patellar tendon shortening and joint line elevation are two main causes of PB. The purpose of this study was to determine the incidence of PB before and after TKA by measuring the patellar height and provide evidence for choosing a suitable index.

METHODS

In total, 256 consecutive patients who underwent primary TKA were included in this study. Radiographic measurements were performed; the Insall-Salvati (IS) index, modified IS (MIS) index, Blackburne-Peel (BP) index, and Caton-Deschamps (CD) index were computed; and the incidence of PB was calculated before and after the operation. The consistency between the IS and MIS indices and between the BP and CD indices was analyzed.

RESULTS

The preoperative incidence of true PB (TPB) and pseudo-PB (PPB) was 9.4 and 0.8%, respectively. The postoperative incidence of TPB and PPB was 10.2 and 9.0%, respectively. The consistency between the IS and MIS indices was moderate preoperatively (pre-kappa = 0.602) and postoperatively (post-kappa = 0.742). The consistency between the BP and CD indices was moderate preoperatively (pre-kappa = 0.742) and good postoperatively (post-kappa = 0.797).

CONCLUSION

The incidence of PB, especially PPB, increased after TKA. The CD and BP indices are of greater importance for the diagnosis of PB after TKA. The MIS index is a better choice than the IS index to measure the length of the patellar tendon. To measure the height of the joint line, the BP index is better postoperatively and the CD index is better preoperatively.

Proximalisation of the tibial tubercle gives a good outcome in patients undergoing revision total knee arthroplasty who have pseudo patella baja

AIMS

The aim of this study was to compare the outcome of revision total knee arthroplasty (TKA) with and without proximalisation of the tibial tubercle in patients with a failed primary TKA who have pseudo patella baja.

PATIENTS AND METHODS

All revision TKAs, performed between January 2008 and November 2013 at a tertiary referral University Orthopaedic Department were retrospectively reviewed. Pseudo patella baja was defined using the modified Insall-Salvati and the Blackburne-Peel ratios. A proximalisation of the tibial tubercle was performed in 13 patients with pseudo patella baja who were matched with a control group of 13 patients for gender, age, height, weight, body mass index, length of surgery and Blackburne-Peel ratio. Outcome was assessed two years post-operatively using the Knee Society Score (KSS).

RESULTS

The increase in KSS was significantly higher in the osteotomy group compared with the control group. The outcome was statistically better in patients in whom proximalisation of > 1 cm had been achieved compared with those in whom the proximalisation was < 1 cm.

CONCLUSION

In this retrospective case-control study, a proximal transfer of the tibial tubercle at revision TKA in patients with pseudo patella baja gives good outcomes without major complications. Cite this article: Bone Joint J 2017;99-B:912-16.

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.

Changes of posterior condylar offset results in midflexion instability in single-radius total knee arthroplasty

INTRODUCTION

There is no algorithm for the management of joint stability in midflexion up to now. Change in the joint line (JL) is considered to be the primary cause, although it only determines the extension gap. The purpose of this study was to determine the influence of the posterior condylar offsets (PCO), which defines the flexion gap, on midflexion instability.

MATERIALS AND METHODS

Forty-two knee joints (38 patients) were included in this study, patients undergoing navigated total knee arthroplasty due to primary osteoarthritis of the knee. Changes in the JL and the PCO were determined from the navigation data. A gap tensioning device was used to determine the width of the joint gap at -5°, 0°, 30° and 60° intraoperatively.

RESULTS

Within a range between 5 mm proximalization and 2 mm distalization, the JL had no influence on stability in midflexion. In contrast to this, both an increase and a decrease in PCO led to midflexion instability (R = 0.361, p = 0.019). In 16 cases (38%), the PCO was changed by more than 2 mm. This led to a midflexion instability of more than 2 mm in seven of these cases (44%).

CONCLUSIONS

Whereas the joint line can be displaced by up to 5 mm without measurable changes in joint stability, reconstruction of the posterior offset within a tight range of 2 mm is necessary to avoid midflexion instability.

Does Patella Tendon Tenodesis Improve Tibial Tubercle Distalization in Treating Patella Alta? A Computational Study

BACKGROUND

Patellofemoral malalignment associated with patella alta may cause pain and arthritis; because of this, the condition sometimes is treated surgically. Two common procedures are tibial tubercle distalization with or without patellar tendon tenodesis. However, the biomechanical consequences of these interventions for patella alta are not clearly understood.

QUESTIONS/PURPOSES

We evaluated changes in patellofemoral joint contact mechanics after tibial tubercle distalization and tibial tubercle distalization combined with patella tendon tenodesis. Specifically, we asked: (1) Are there biomechanical differences between these two types of procedures? (2) Is there an ideal range to distalize the patella?

METHODS

Subject-specific finite-element models were created for 10 individuals with patella alta (mean Insall-Salvati ratio of 1.34 ± 0.05). Input parameters for the finite-element models included subject-specific joint geometry, quadriceps muscle forces, and weightbearing patellofemoral joint kinematics. Virtual operations were conducted to simulate the two procedures. For distalization, the tibial tubercle and patella were displaced distally 4 mm to 20 mm in 4-mm increments based on the original model. At each level of distalization, the patella tendon was attached back to its original insertion to simulate the additional tenodesis procedure. Cartilage stress, contact area, and contact forces were quantified and compared between procedures and distalization levels.

RESULTS

Distalization and distalization + tenodesis reduced patellofemoral joint stress compared with the baseline of 1.02 ± 0.11 MPa. Distalization led to lower cartilage stress than distalization + tenodesis, and the effect size was relatively large (0.88 ± 0.10 MPa vs 0.92 ± 0.10 MPa; mean difference, 0.04 MPa [95% CI, 0.02 MPa-0.05 MPa], p < 0.01; effect size of 1.64 [Cohen's d], with Insall-Salvati ratio decreased to 0.95). For both procedures, the trend of stress reduction plateaued when the Install-Salvati ratio approached 0.95.

CONCLUSIONS

Cartilage stress appears lower using distalization as opposed to distalization + tenodesis in this finite-element analysis simulation. An Insall-Salvati ratio of 0.95 may be an ideal level for distalization; further distalization does not show additional benefits.

CLINICAL RELEVANCE

This study suggests that distalization may result in less stress than distalization + tenodesis, therefore future clinical research might be preferentially directed toward evaluating isolated distalization procedures.

Evidence of patellar tendon buckling during passive knee extension

PURPOSE

The purpose of this study was to investigate and describe buckling of the patellar tendon.

METHODS

Healthy young adults (28±4years, 10F/10M) underwent passive knee flexion/extension during the simultaneous measurement of knee angle and collection of cine ultrasound from the patellar tendon. Patellar tendon buckling was observed visually in ultrasound images, and the corresponding knee angle at which evidence of buckling disappeared was identified.

RESULTS

All subjects showed evidence of distal buckling which occurred on average at 23±8° flexion. Proximal buckling was only observed in fourteen subjects (10F/4M) at an average of 15±8°. Buckling patterns varied between subjects, but with high within-subject consistency. Buckling magnitude increased with age (p=0.03) and decreased with more weekly exercise (p=0.02).

DISCUSSION

The patellar tendon exhibited significant buckling in knee extension suggesting that buckling is a component of healthy knee function. Like tendon crimp, buckling may serve as a protective mechanism, allowing the tissue to unwrinkle prior to undergoing pure strain. The links between increased buckling magnitude and both age and reduced activity suggest that excessive buckling may be maladaptive, though future work is necessary to elucidate this relationship. Buckling is relevant to consider when estimating tendon length, as buckling can lead to significant underestimation of resting length and thus overestimation of strain.

CONCLUSION

This study demonstrates the complexity of tendon behavior even in healthy adults undergoing passive motion, suggesting that buckling may be relevant to an improved understanding of tendon health and pathology.

Effect of Joint Line Elevation after Posterior-stabilized and Cruciate-retaining Total Knee Arthroplasty on Clinical Function and Kinematics

BACKGROUND

Joint line (JL) is a very important factor for total knee arthroplasty (TKA) to restore. The objective of this study was to evaluate the early clinical and kinematic results of TKAs with posterior-stabilized (PS) or cruciate retaining (CR) implants in which the JL was elevated postoperatively.

METHODS

Data were collected from patients who underwent TKA in our department between April 2011 and April 2014. The patients were divided into two groups based on the prosthesis they received (PS or CR). At 1-year postoperatively, clinical outcomes were evaluated by the American Knee Society (AKS) knee score, AKS function score, and patella score. In vivo kinematic analysis after TKA was performed on all patients and a previously validated three-dimensional to two-dimensional image registration technique was used to obtain the kinematic data. Anteroposterior (AP) translation of the medial and lateral femoral condyles, and axial rotation relative to the tibial plateau, were analyzed. The data were assessed using the Mann-Whitney test.

RESULTS

At time of follow-up, there were differences in the AKS knee scores (P = 0.005), AKS function scores (P = 0.025), patella scores (P = 0.015), and postoperative range of motions (P = 0.004) between the PS group and the CR group. In the PS group, the magnitude of AP translation for the medial and lateral condyle was 4.9 ± 3.0 mm and 12.8 ± 3.3 mm, respectively. Axial rotation of the tibial component relative to the femoral component was 12.9 ± 4.5°. In the CR group, the magnitude of AP translation for the medial and lateral condyle was 4.3 ± 3.5 mm and 7.9 ± 4.2 mm, respectively. The axial rotation was 6.7 ± 5.9°. There were statistically different between PS group and CR group in kinematics postoperatively.

CONCLUSION

Our results demonstrate that postoperative JL elevation had more adverse effects on the clinical and kinematic outcomes of CR TKAs than PS TKAs.

Patellar Height Decreasing After Distal Femur Endoprosthesis Reconstruction Does Not Affect Functional Outcome

INTRODUCTION

The patellar height can influence extensor mechanism and the knee function. Thus, during knee arthroplasty, the surgeon seeks to maintain the correct patellar height. However, it is more difficult to define and maintain the correct patella height in megaprosthesis reconstructions after tumor resections. The objective of this study was to evaluate patellar height after distal femur endoprosthesis reconstruction and its association to knee function.

METHODS

This retrospective analysis included 108 patients who underwent distal femur resections and endoprosthesis reconstruction. The minimum follow-up was 1 year or until the patients underwent patellar resurfacing or endoprosthesis revision. Patellar height was calculated using Insall-Salvati ratio (ISR) and Insall-Salvati patellar tendon insertion ratio (PTR) at 2 different times: postoperatively and at the final follow-up. The postoperative ratio was calculated using the best postoperative radiograph taken at least 1 month after the procedure. The final measures were based on the radiograph available at the last follow-up consultation. The ISR and PTR were associated to anterior knee pain (AKP), range of motion (ROM), and extension lag (EXL).

RESULTS

The average follow-up was 4.5years. The mean postoperative ISR was 1.02, and the mean ISR at final follow-up was 0.95 (P<.0001). The mean postoperative PTR was 1.45, and the mean PTR at final follow-up was 1.40 (P=.016). There was no association between patellar height and AKP, ROM, and EXL. Patellar height decreases significantly after distal femur resections but does not affect AKP, ROM, and EXL.

Patient-Specific Total Knees Demonstrate a Higher Manipulation Rate Compared to "Off-the-Shelf Implants"

Patient-specific total knee replacements have been designed in hopes of providing better functional outcomes compared to "off-the-shelf" implants in primary total knee arthroplasty (TKA). We prospectively evaluated manipulation rates and clinical outcomes of 21 patient-specific TKAs matched with 42 posterior-stabilized and 11 cruciate-retaining "off-the-shelf" TKAs. Postoperatively, the patient-specific group had a range of motion significantly less than both control groups (P<0.01). Six of the 21 (28.6%) patient-specific TKAs required manipulation to improve range of motion. No manipulations were reported in either control groups. At minimum two-year follow-up the patient-specific TKAs had similar motion, but worse satisfaction and KSS pain scores. Radiographic analysis provided no insight to the cause of stiffness. Early manipulation is recommended for stiffness with patient-specific TKA.

Prevention of pseudo-patella baja during total knee arthroplasty

PURPOSE

Pseudo-patella baja (PPB) is a surgical complication that can arise from total knee arthroplasty and occurs when the patella tendon is not shortened but the level of the femorotibial joint line is elevated. The goal of this study was to assess the performance of a technique specifically designed to prevent the occurrence of PPB and its radiological results.

METHODS

Ninety-nine patients undergoing total knee arthroplasty were included. Patients were divided into a non-correction group and a correction group. The correction group were applied an additional metal block in order to reduce the excess resection of the distal femur. To evaluate PPB, the change in the pre- and postoperative joint line was measured using the modified Blackburne-Peel Index (BPI).

RESULTS

In the non-correction group, 68 of 74 cases showed an occurrence of PPB (92 %), in the correction group, 6 of 57 cases showed an occurrence of PPB (11 %). The preoperative-modified BPI of the non-correction group was not significantly different from that of the correction group (0.6 ± 0.1 vs. 0.6 ± 0.2). The modified BPI decreased significantly in the non-correction group after TKA (0.6 ± 0.1 vs. 0.2 ± 0.1, p < 0.05). However, the modified BPI did not change significantly in the correction group after TKA (0.6 ± 0.2 vs. 0.6 ± 0.2).

CONCLUSION

The comparison of preoperative and postoperative radiological results showed that our intervention maintained the joint line without elevation. We proposed an effective method to prevent various complications due to the joint line elevation that occur in PPB.

LEVEL OF EVIDENCE

III.

Efficacy and Safety of Tranexamic Acid in Bilateral Total Knee Replacement: A Meta-Analysis and Systematic Review

Background

Tranexamic acid (TXA) has been well documented to reduce blood loss and transfusion requirements in patients undergoing unilateral total knee arthroplasty (TKA). However, the efficacy and safety of TXA in simultaneous bilateral TKA have not been clearly defined. The aim of our study was to systematically review the existing evidence regarding the role of TXA in patients undergoing simultaneous bilateral TKA.

Material/Methods

A systematic search of all studies published through June 2014 was performed using Medline, EMBASE, OVID, and other databases. All studies that compared the efficacy and safety of TXA administration in simultaneous bilateral TKA patients were identified. The data from the included trials were extracted and analyzed regarding blood loss and transfusion rates. The evidence quality levels of the selected articles were evaluated using a grading system.

Results

Six studies were included, in which a total of 245 patients received TXA and 271 patients were controls. Overall, the results demonstrated that the use of TXA significantly reduced total blood loss by a mean of 371.1 ml (95% confidence interval (CI)=−412.12 to −330.09; p<0.001) and reduced the number of patients requiring blood transfusion (risk ratio (RR)=0.16; 95% CI=0.10 to 0.28; p<0.001). No significant differences in adverse effects such as deep vein thrombosis (DVT) or pulmonary embolism (PE) were noted in any group.

Conclusions

The intravenous use of TXA in patients undergoing simultaneous bilateral TKA is effective and safe and results in significantly reduced estimated blood loss and transfusion rates. No significant difference was observed in the incidence of side effects. Due to the limitations in the evidence quality of current meta-analyses, well-conducted, larger, high-quality randomized controlled trials (RCTs) are required.

Proximalize osteotomy of tibial tuberosity (POTT) as a treatment for stiffness secondary to patella baja in total knee arthroplasty (TKA)

INTRODUCTION

Stiffness after a total knee arthroplasty (TKA) is one of the most common post-operative complications. The purpose of this study is the evaluation of the effectiveness of TT proximalization osteotomy of improving a lack of flexion and secondary pain in patella baja (infera) post-TKA.

MATERIALS AND METHODS

Between April 2007 and July 2012, TT proximalization osteotomy was performed on 21 patients. The average preoperative flexion was 70° (in a range of 60-80). Clinical pre- and post-operative evaluations were performed with Knee Society Score, Western Ontario and McMaster Universities Arthritis Index scales and a satisfaction survey. Modified Blackburn-Peel index and Portner angle were used to evaluate patellar height.

RESULTS

After an average follow-up of 35 months (range 18-48), an average flexion of 100° (range 90-100) and an overall satisfaction were obtained. Clinical scores improved significantly. The Blackburn-Peel index and Portner angle improved significantly from 0.3 (range 0.1-0.5) to 0.4 (0.3-0.5) and from 9 (3-15) to 12 (9-18), respectively. Three patients showed no signs of osteotomy consolidation. However, this was not linked to a lack of extension or an increase in local pain.

CONCLUSION

TT proximalization osteotomy provides satisfactory results in improving a lack of flexion and pain in patella baja post-TKR.

Joint line changes in cruciate-retaining versus posterior-stabilized computer-navigated total knee arthroplasty

INTRODUCTION

This study compared joint line changes and functional outcomes between cruciate-retaining (CR) and posterior-stabilized (PS) computer-navigated total knee arthroplasties (TKAs). With the increased precision offered by computer navigation, we hypothesized that there should be minimal differences in the joint line changes between the groups and thus no significant differences in the clinical outcomes.

MATERIALS AND METHODS

A retrospective study of 195 patients with a minimum of 2-year follow-up following primary surgery was conducted. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups.

RESULTS

CR knees had a significantly lesser mean joint line change of 1.70 mm as compared to 2.34 mm in PS knees (p = .04) but the absolute difference was only 0.64 mm. The PS group had significantly better final range of motion of 122° (±9.9°) as compared to 114° (±15.0°) in the CR group (p < .0001). There were no significant differences in the final outcome scores.

CONCLUSION

Although there is a significant difference statistically in the joint line changes between the groups, this difference is less than 1 mm and probably has no significant clinical impact. This is further affirmed by the fact that there was no significant difference in the clinical outcomes. The increased range seen in PS knees is probably not related to joint line changes.

LEVEL OF EVIDENCE

III.

A case-control study of spontaneous patellar fractures following primary total knee replacement

Peri-prosthetic patellar fracture following resurfacing as part of total knee replacement (TKR) is an infrequent yet challenging complication. This case-control study was performed to identify clinical, radiological and surgical factors that increase the risk of developing a spontaneous patellar fracture after TKR. Patellar fractures were identified in 74 patients (88 knees) from a series of 7866 consecutive TKRs conducted between 1998 and 2009. After excluding those with a previous history of extensor mechanism realignment or a clear traumatic event, a metal-backed patella, any uncemented component or subsequent infection, the remaining 64 fractures were compared with a matched group of TKRs with an excellent outcome defined by the Knee Society score. The mean age of patients with a fracture was 70 years (51 to 81) at the time of TKR. Patellar fractures were detected at a mean of 13.4 months (2 to 84) after surgery. The incidence of patellar fracture was found to be strongly associated with the number of previous knee operations, greater pre-operative mechanical malalignment, smaller post-operative patellar tendon length, thinner post-resection patellar thickness, and a lower post-operative Insall-Salvati ratio.

An understanding of the risk factors associated with spontaneous patellar fracture following TKR provides a valuable insight into prevention of this challenging complication.