Miho J. Tanaka

Technical Failure of Medial Patellofemoral Ligament Reconstruction

In patients with chronic patellofemoral instability who have normal alignment and deficient proximal medial restraints, medial patellofemoral ligament (MPFL) reconstruction is a good option to treat patellar instability. However, medial subluxation, medial patellofemoral articular overload, and recurrent lateral instability are possible when the graft is positioned non-anatomically. The clinical presentation of MPFL femoral tunnel malpositioning has not been highlighted in the literature. We have had 5 patients referred to us after a malpositioned femoral MPFL graft led to disabling symptoms and a need for revision surgery. This report highlights the effects of a malpositioned graft and describes strategies to identify the anatomic MPFL insertion during surgery.

Hamstrings Loading Contributes to Lateral Patellofemoral Malalignment and Elevated Cartilage Pressures: An In Vitro Study

BACKGROUND Hamstrings loading has previously been shown to increase tibiofemoral posterior translation and external rotation, which could contribute to patellofemoral malalignment and elevated patellofemoral pressures. The current study characterizes the influence of forces applied by the hamstrings on patellofemoral kinematics and the pressure applied to patellofemoral cartilage. METHODS Ten knees were positioned at 40°, 60° and 80° of flexion in vitro, and loaded with 586 N applied through the quadriceps, with and without an additional 200 N applied through the hamstrings. Patellofemoral kinematics were characterized with magnetic sensors fixed to the patella and the femur, while the pressure applied to lateral and medial patellofemoral cartilage was measured with pressure sensors. A repeated measures ANOVA with three levels, combined with paired t-tests at each flexion angle, determined if loading the hamstrings significantly (P<0.05) influenced the output. FINDINGS Loading the hamstrings increased the average patellar flexion, lateral tilt and lateral shift by approximately 1°, 0.5° and 0.2mm, respectively. Each increase was significant for at least two flexion angles. Loading the hamstrings increased the percentage of the total contact force applied to lateral cartilage by approximately 5%, which was significant at each flexion angle, and the maximum lateral pressure by approximately 0.3 MPa, which was significant at 40° and 60°. INTERPRETATION The increased lateral shift and tilt of the patella caused by loading the hamstrings can contribute to lateral malalignment and shifts pressure toward the lateral facet of the patella, which could contribute to overloading of lateral cartilage.

Correlation Between Changes in Tibial Tuberosity–Trochlear Groove Distance and Patellar Position During Active Knee Extension on Dynamic Kinematic Computed Tomographic Imaging

PURPOSE The purpose of this study was to evaluate changes in tibial tuberosity-trochlear groove (TTTG) distance with knee flexion in patients with patellar instability and correlate it with patellar position. METHODS Patients with symptomatic patellar instability underwent dynamic kinematic computed tomography (CT) during a cycle of knee extension from flexion. Knee flexion angles and corresponding TTTG distances, bisect offset, and patellar tilt were measured. Of the 51 knees, 37 had data available for interpolation between 5° and 30°. Results were interpolated to standardized intervals between 5° and 30° of knee flexion. Repeated-measures analysis (to identify differences between TTTG measurements at various knee flexion angles) and linear regression models (to assess for correlations between TTTG distance and bisect offset and between TTTG distance and patellar tilt) were used. RESULTS Fifty-one symptomatic knees in 38 patients were available for analysis. Bisect offset and patellar tilt correlated significantly (P < .001) with TTTG distance over all flexion angles. Interpolated results for comparison resulted in 37 knees in which the mean TTTG distance of 17.2 ± 5.8 mm at 5° decreased to 15.5 ± 5.7, 13.0 ± 5.5, and 11.5 ± 4.9 mm at 10°, 20°, and 30° of knee flexion, respectively. Mean TTTG at 5° was 1.5 times greater than that at 30° (P < .001). At 5°, 70.3% (26 of 37) of knees had a TTTG distance of more than 15 mm; at 30°, only 24.3% (9 of 37) exceeded this threshold. CONCLUSIONS Knee flexion angle during imaging is a critical factor when measuring TTTG distance to evaluate patellofemoral instability. We found that the mean TTTG distance varied by 5.7 mm between 5° and 30° of flexion in patients with symptomatic instability, although this relationship was not completely linear. Bisect offset and patellar tilt measurements mirrored this pattern, suggesting that TTTG distance influences patellar tracking in these patients. LEVEL OF EVIDENCE Level IV, prognostic case series.

The Relationship Between Tibial Tuberosity-Trochlear Groove Distance and Abnormal Patellar Tracking in Patients With Unilateral Patellar Instability.

PURPOSE To evaluate the role of tibial tuberosity-trochlear groove (TT-TG) distance in patellofemoral kinematics by retrospectively reviewing the dynamic computed tomography scans of patients with unilateral patellofemoral instability and comparing unstable and contralateral asymptomatic knees. METHODS We reviewed all dynamic computed tomography scans obtained at one tertiary care hospital from 2008 through 2013 and identified 25 patients with a history of recurrent unilateral patellofemoral instability. During the scans, subjects performed active knee extension against gravity. Both knees were imaged simultaneously. Lateral patellar tilt (LPT) and bisect offset (BO) were measured to assess tracking. TT-TG distance was measured to assess alignment. Measurements were made in full extension, maximum flexion, and approximately 10° increments in between. The significance level was set at P < .05. RESULTS LPT, BO, and TT-TG distance were highest in extension and decreased with flexion. Measurements were higher in symptomatic than in asymptomatic knees, with significant differences identified for LPT, BO, and TT-TG distance at 5° and 15° and for TT-TG distance at 25° and 35° (P < .05). TT-TG distance was associated with LPT and BO, with r(2) values in symptomatic knees of 0.55 for TT-TG distance and LPT and of 0.45 for TT-TG distance and BO. CONCLUSIONS In patients with unilateral patellar instability, LPT, BO, and TT-TG distance are higher on the unstable side. An association exists between TT-TG distance and the tracking parameters studied, suggesting that TT-TG distance relates to patellar tracking, and a laterally positioned tibial tuberosity may predispose to instability episodes. LEVEL OF EVIDENCE Level IV, diagnostic study.

The Anatomic Midpoint of the Attachment of the Medial Patellofemoral Complex

BACKGROUND The medial patellofemoral ligament varies in attachment of its fibers to the patella and vastus intermedius tendon. Our aim was to identify and describe its anatomic midpoint. To account for the variability of the attachment site, we refer to it as the medial patellofemoral complex. METHODS Using AutoCAD software, we identified the midpoint of the medial patellofemoral complex attachment on photographs of 31 cadaveric knee dissections. The midpoint was referenced relative to the superior articular surface of the patella (P1) and was described in terms of the percentage of the patellar articular length distal to this point. A second point, at the junction of the medial border of the vastus intermedius tendon with the superior articular border of the patella, was identified (P2). The distances of the midpoint to P1 and P2 were calculated and were compared using paired t tests. RESULTS Twenty-five images had appropriate quality and landmarks for digital analysis. The midpoint of the medial patellofemoral complex was located a mean (and standard deviation) of 2.3% ± 15.8% of the patellar articular length distal to the superior pole and was at or proximal to P1 in 12 knees. In all knees, the midpoint was at or proximal to P2. After exclusion of 2 knees with vastus intermedius tendon attachments only, the medial patellofemoral complex midpoint was closer to P2 (5.3% ± 8.6% of the patellar articular length) than to P1 (9.3% ± 8.5% of the patellar articular length) (p = 0.06). CONCLUSIONS The midpoint of the medial patellofemoral complex was 2.3% of the articular length distal to the superior pole of the patella. Additionally, we describe an anatomic landmark at the junction of the medial border of the vastus intermedius tendon and the articular border of the patella that approximates the midpoint of this complex. CLINICAL RELEVANCE Our study shows that the anatomic midpoint of the attachment of the medial patellofemoral complex is proximal to the junction of the medial vastus intermedius tendon and the articular border of the patella, suggesting that graft placement may be more anatomic on the vastus intermedius tendon rather than on the patella.

Incidence of Deep Venous Thrombosis After Tibial Tubercle Osteotomy A Single Case Series Study

Background: Tibial tubercle osteotomy (TTO) is performed in a predominantly young and often female population due to the prevalence of patellofemoral disorders in this group. While considered a procedure that falls within the realm of sports surgeries, the procedure can carry significant morbidity, including infection, fracture, and deep vein thrombosis (DVT). The incidence of postoperative DVT in this population has not been described in the literature, although it has been mentioned anecdotally, and current guidelines do not address the issue of DVT prophylaxis in postoperative TTO patients. Purpose: To describe the incidence of DVT after TTO and identify any predisposing factors. Study Design: Case series; Level of evidence, 4. Methods: Subjects who had undergone TTO by the senior author from 2002 to 2013 were identified, and a retrospective chart review was performed. Those who presented with symptomatic DVT confirmed with ultrasonography were reported. Demographic data, as well as potential risk factors such as body mass index, family history of bleeding/clotting disorders, duration of the nonweightbearing period, total tourniquet time, use of contraceptive medication, smoking status, and use of anticoagulants, were collected from the chart and analyzed for correlation with development of DVT. Results: A total of 156 patients were included in this study. Six patients were found to have developed symptomatic DVT during the first 6 weeks after surgery. The mean age at the time of surgery in the DVT group was 34.94 ± 6.57 years, compared with 26.26 ± 10.20 years in the non-DVT group (P = .04). Due to the small number of patients with positive findings, there was no statistically significant correlation between the development of DVT and factors such as nonweightbearing duration, tourniquet time, or the use of contraceptives. Conclusion: The incidence of postoperative DVT in arthroscopic and sports procedures has been thought to be low. This case series reported a rate of 3.8% with symptomatic DVT after TTO, and patients diagnosed with DVT were significantly older than unaffected patients. It is anticipated that the actual rate including asymptomatic DVT would be higher, as only 60% of patients with DVT are symptomatic. More studies are needed to define the actual incidence in this population. Given the number of common risk factors in this population, including nonweightbearing duration and the use of oral contraceptive pills, future studies may show the advantage of chemical prophylaxis for DVT in this group.

The Anatomy of the Medial Patellofemoral Complex

The term “medial patellofemoral complex” (MPFC) was proposed to describe the static medial stabilizer of the patella, typically referred to as the medial patellofemoral ligament. In light of our increasing understanding of the attachment of its fibers to the quadriceps tendon in addition to the patella, the term MPFC is used in this article. The purpose of this article is to describe and discuss the anatomy of the MPFC.

When and How Far to Move the Tibial Tuberosity in Patients With Patellar Instability

The many factors contributing to patellar instability have led to various surgical techniques that are used commonly today. When surgery is deemed necessary, the operation should be tailored to the patient’s specific pathoanatomy. Patients with malalignment can often be stabilized by moving the tibial tuberosity to a more medial, anteromedial, or distal position. Subsequent changes in the forces acting on the patellofemoral joint will depend on the direction and distance of the tuberosity repositioning. When planning tuberosity osteotomies, it is crucial to understand how to use clinical and imaging modalities to measure and quantify tuberosity position accurately to achieve the desired degree of realignment.

Rehabilitation After Medial Patellofemoral Ligament Reconstruction

Patellar instability resulting from subluxation or dislocation is a painful and commonly recurring condition. Retinacular restraints control patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is considered the main soft tissue stabilizer against lateral displacement. Few studies of patellar instability discuss rehabilitation after MPFL reconstruction. In this review, we discuss the phases of rehabilitation after MPFL reconstruction, typical interventions by rehabilitation specialists, and patient-specific guidelines for return to prior level of function. The Musculoskeletal Institute at The Johns Hopkins Hospital (a collaboration of orthopedic surgeons, primary care sports medicine physicians, and clinicians from the Department of Physical Medicine and Rehabilitation) presents its rehabilitation protocol with phase-specific guidelines for progression after MPFL reconstruction. This evidence-based protocol is a generalized approach that is customized for each patient’s needs.

Characterizing Patterns In Patellar Maltracking On Dynamic Kinematic CT Imaging

Objectives: Patellar maltracking has been traditionally difficult to assess due to its dynamic component. Unlike the assessment of malalignment, which relies on static radiographic measurements, maltracking is a dynamic phenomenon described subjectively with the J sign. The advent of dynamic, kinematic computed tomographic imaging (DKCT) has allowed for the dynamic assessment of the patellofemoral joint. We used DKCT to visualize and quantify patterns of patellar maltracking and correlated these findings with the presence or absence of symptoms of patellar instability. Methods: 76 knees in 38 subjects were analyzed using DKCT. Measurements of bisect offset at 10° intervals of knee flexion were performed for each knee during active flexion/extension cycles. Patterns in bisect offset were assessed and graded in terms of 1, 2 or 3 quadrants of lateral patellar motion, based on 75-100, 100-125, and >125% bisect offset. The presence or absence of symptomatic patellar instability were recorded for each knee, and ratios of patients with symptoms were calculated for J sign tracking patterns of grades 1, 2 and 3. Differences in ratios between Grades 1, 2 and 3 were calculated using chi squared analysis. Results: 76 knees were available for analysis, of which 51 had symptomatic patellar instability. 9 knees demonstrated normal patterns of tracking. 58 knees demonstrated increased lateral translation in extension. 7 knees showed persistent lateralization of the patella throughout range of motion, and 2 knees showed increased translation in flexion. In the 58 knees that showed maximal lateral translation in extension (J sign), the J sign was graded as 1(N=24), 2 (N=20) and 3 (N=14). The sensitivities of J sign grades in predicting patellar instability were 45.8% (J1), 80% (J2), and 92.9% (J3) (p<0.01), with statistically significant differences between Grades 1 and 2/3 (0=0.018). Conclusion: On DKCT imaging, we noted additional patterns of patellar maltracking besides the standard J sign. Of those with maltracking in extension (J sign), Grade 2 and 3 J signs with > 2 quadrants of patellar lateralization in extension were predictive of symptomatic patellar instability. Further understanding of patellar maltracking patterns can provide the clinician with information regarding the pathoanatomy and pathophysiology of patellar instability, and allow us to better plan for surgical stabilization.