Knee biomechanics during squat rising with patella alta and after distal transfer of tibial tubercular surgery

Patella alta has commonly seen in prior adolescent cerebral palsy population with crouch gait pattern. Unfortunately, for the treatments of PA and crouch gait, the outcomes of physical therapy, orthotic and surgical treatments are highly questionable. The purpose of this study is to investigate the effects of patella alta on knee biomechanics and to analyze the benefits of distal transfer of tibial tubercule (DTTT) during dual limb knee squat extension. A three-dimensional dynamic knee model comprising patellofemoral and tibiofemoral joints was developed. Patellar tendon length was increased 25% and 50% of its original length to simulate the patology. Tibiofemoral and patellofemoral contact forces, loads on ligament bundles, tibial rotations and quadriceps efficiencies were compared for patology, normal and after DTTT surgery (DTTTS). The results showed that patella alta, increases the tibiofemoral and patellofemoral compressive force, alters the neutral tension of ligament bundles, reduces the medio-lateral knee stability and increases the efficiency of the quadriceps muscle during squat rising. Even though DTTTS normalized some of the biomechanical alterations, internal rotation in higher flexion angles, valgus-varus rotation of the tibia and the tension of aACL and PCL remained different than normal. These alterations may play a contributory role to develop cartilage degeneration on tibiofemoral and patellofermoral joints. Inadequate quadriceps force and abnormal loading pattern on some of the ligaments may also contribute to the recurrence mechanism of crouch gait after DTTTS surgery.

Patellar Tendon Imbrication Is a Safe and Efficacious Technique to Shorten the Patellar Tendon in Patients With Patella Alta

Background: Patella alta has been noted to be a risk factor for recurrent patellar instability. Purpose: We conducted a radiographic study to determine whether a patellar tendon imbrication technique normalizes patellar height as well as whether the shortened length is maintained at a minimum 2-year follow-up. Study Design: Case series; Level of evidence, 4. Methods: A total of 54 consecutive patients were identified after a retrospective chart review was performed on patients who underwent patellar tendon imbrication between 2008 and 2013. Preoperative, 3 weeks postoperative, and minimum 2 years postoperative lateral radiographs were analyzed using Insall-Salvati (IS), Blackburne-Peel (BP), and Caton-Deschamps (CD) indices to determine the amount of shortening that was achieved after the procedure and to what degree that shortening was maintained at a minimum 2-year follow-up. Results: A total of 27 patients (32 knees) completed a minimum 2-year follow-up. The mean patellar tendon length preoperatively was 6.1 cm (range, 5-8 cm). At 3 weeks and 2 years, the mean tendon lengths were 5.1 and 5.2 cm, respectively. Thus, the mean ± SD change in patellar tendon length from preoperative to 3 weeks postoperative was 0.97 ± 0.67 cm. IS, BP, and CD ratios had minimal change (loss of correction) from 3-week to 2-year follow-up; the delta values were 0.04, –0.03, and 0.09, respectively. There were no complications directly related to the technique. Conclusion: Patellar tendon imbrication is a safe and effective procedure to correct patella alta in the setting of lateral patellar instability. On average, the technique allowed 1 cm of patellar tendon shortening and maintained the correction at a minimum 2-year follow-up. In the skeletally immature patient, this technique allows correction of patella alta by avoidance of a tibial tuberosity osteotomy.

Associations between Anterior Cruciate Ligament Injuries and Patella Alta and Trochlear Dysplasia in Adults Using Magnetic Resonance Imaging

The aim of this study was to research the associations between anterior cruciate ligament (ACL) injuries and patella alta and trochlear dysplasia in adult patients using magnetic resonance imaging (MRI). This retrospective study included 221 adult patients: 110 with acute complete noncontact ACL tears and 111 without ACL injuries who underwent knee MRI procedures between May 2016 and July 2018. After the ACL injuries were verified using the sagittal proton density images, the patellar height and patellar tendon length were measured on the sagittal T1-weighted images, and the Insall–Salvati ratio (ISR) was calculated. In the axial proton density MRI scans, according to the Dejour and Le Coultre classification of trochlear dysplasia, the knees were classified as normal or as types A, B, C, or D. The patellar length was not significantly different between the patient and control groups (41.5 ± 3.3 vs. 41.0 ± 2.9 mm, respectively). An increased patellar tendon length (46.1 ± 3.9 vs. 44.5 ± 3.4 mm, respectively) and an increased ISR (1.11 ± 0.08 vs. 1.08 ± 0.06, respectively) were measured in the patient group (with the ACL tears). In the group with the ACL tears, the rate of trochlear dysplasia was higher (15.45%) than that in the healthy group (4.5%). Of the 17 trochlear dysplasia patients in the ACL group, 11 were type A (10%), 2 were type B (1.82%), 3 were type C (2.73%), and 1 was type D (0.91%). Results showed increased patellar tendon lengths, ISRs, and trochlear dysplasia in the patients with the ACL injuries when compared with the healthy control group. Although the causative relationship has not yet been clearly elucidated, one should keep in mind that these variations may be risk factors for ACL tears.

Patellar Impingement on Tibial Polyethylene after Primary Total Knee Arthroplasty without Patellar Resurfacing

Patellar impingement on tibial polyethylene (PIP) is one potential complication of total knee arthroplasty (TKA). When PIP occurs, it is often related to inaccurate restoration of the joint line or due to soft-tissue contracture. We investigated the prevalence and etiology of PIP in Asian patients with deeply flexed knees following posterior stabilized (PS)-TKA. We retrospectively reviewed 54 patients (65 knees) with PIP after primary PS-TKAs without patellar resurfacing performed between 2008 and 2011. These patients were compared with a group of 124 patients (130 knees) without PIP matched for age, sex, and body mass index (BMI). The minimum follow-up was 5 years (range, 5–8.1 years). Patients were evaluated by blinded, independent observers using the Oxford knee score, the Waters score, and radiographic parameters. Impingement between the patella and the tibial polyethylene had a mean onset of 13.5 months after PS-TKA. The development of PIP was significantly associated with change in patellar tendon length (odds ratio [OR] = 11.4, 95% confidence interval [CI]: 11.2–11.6%), shorter postoperative patellar tendon length (OR = 2.1, 95% CI: 1.8–2.5%), change in the Insall–Salvati ratio (OR = 0.9, 95% CI: 0.8–1.0%), and joint line elevation (OR = 5.3, 95% CI: 4.8–5.8%) on multiple logistic regression analysis. Our findings reinforce the importance of accurate joint line restoration and the avoidance of iatrogenic injury to the patellar tendon, which can lead to shortening of the patellar tendon. This is a retrospective comparative study and its level of evidence is III.