Zone of injury of the medial patellofemoral ligament after acute patellar dislocation in children and adolescents

BACKGROUND

Patellar dislocation is a common traumatic injury in the pediatric and adolescent population. The primary constraint to lateral subluxation and dislocation of the patella is the medial patellofemoral ligament (MPFL), which serves to resist lateral translation of the patella. Injury to the MPFL may predispose to recurrent dislocation but the anatomic site of injury is poorly characterized in children and adolescents.

PURPOSE

The authors addressed 2 questions: (1) What is the zone of injury to the MPFL in a pediatric/adolescent population after primary patellar dislocation? (2) What is the location of the femoral attachment of the MPFL with respect to the growth plate?

STUDY DESIGN

Cohort study (prevalence); Level of evidence, 2.

METHODS

Patients were eligible if they were ≤18 years of age and suffered a recent patellar dislocation characterized by magnetic resonance imaging (MRI) findings of high T2-signal intensity in the lateral femoral condyle. Patients were excluded if they had a history of prior dislocations, prior knee surgery, or congenital dislocation. Two musculoskeletal radiologists and an orthopaedic resident reviewed MRI scans of 43 children. The MPFL was divided into 3 zones: patellar insertion, femoral insertion, and midsubstance. The zone of injury was confirmed by the presence of associated soft tissue edema on short tau inversion recovery sequences and the distance from the MPFL insertion to the medial distal femoral growth plate was measured. Associated injuries were noted and the Insall-Salvati ratio was measured.

RESULTS

The MPFL injury was isolated to the patellar attachment in 61% of patients and to the femoral attachment in 12%. Twelve percent of patients had injury at both the patellar and femoral attachments. Six percent had no identifiable MPFL injury and 9% had combinations of midsubstance and either patellar or femoral attachment injuries. The kappa value for injury determinations was 0.71, indicating substantial concordance. The MPFL insertion site averaged 5 mm distal to the medial physis. Eighty-six percent of patients had an MPFL insertion distal to the growth plate, 7% had an insertion at the physis, while only 7% had a proximal insertion. The incidence of associated chondral injuries, the value of the Insall-Salvati ratio, and the location of MPFL insertion did not vary significantly with location of MPFL injury. Sixteen patients (36%) had MPFL insertions that were within 5 mm (either proximal or distal) of the growth plate.

CONCLUSION

The zone of MPFL injury in a pediatric population after primary patellar dislocation was predominantly isolated to the patellar attachment (61%), in contrast to previous literature. Twelve percent of patients had injury only at the femoral attachment, while 12% of patients had injury to both the patellar and femoral attachments. The remaining 15% had injury at multiple locations or no identifiable injury. The MRI finding that the anatomic insertion of the MPFL is distal to the physis in 93% of patients and that the MPFL is more likely to be injured at the patellar attachment has important implications in the surgical reconstruction of the MPFL in pediatric or adolescent patients.

Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion

Lateral transpsoas interbody fusion (LTIF) is a minimally invasive technique that permits interbody fusion utilizing cages placed via a direct lateral retroperitoneal approach. We sought to describe the locations of relevant neurovascular structures based on MRI with respect to this novel surgical approach. We retrospectively reviewed consecutive lumbosacral spine MRI scans in 43 skeletally mature adults. MRI scans were independently reviewed by two readers to identify the location of the psoas muscle, lumbar plexus, femoral nerve, inferior vena cava and right iliac vein. Structures potentially at risk for injury were identified by: a distance from the anterior aspect of the adjacent vertebral bodies of <20 mm, representing the minimum retraction necessary for cage placement, and extension of vascular structures posterior to the anterior vertebral body, requiring anterior retraction. The percentage of patients with neurovascular structures at risk for left-sided approaches was 2.3% at L1-2, 7.0% at L2-3, 4.7% at L3-4 and 20.9% at L4-5. For right-sided approaches, this rose to 7.0% at L1-2, 7.0% at L2-3, 9.3% at L3-4 and 44.2% at L4-5, largely because of the relatively posterior right-sided vasculature. A relationship between the position of psoas muscle and lumbar plexus is described which allows use of the psoas position as a proxy for lumbar plexus position to identify patients who may be at risk, particularly at the L4-5 level. Further study will establish the clinical relevance of these measurements and the ability of neurovascular structures to be retracted without significant injury.

Vertebral body fracture after anterolateral instrumentation and interbody fusion in two osteoporotic patients

BACKGROUND CONTEXT

The XLP plate is an anterolateral instrumentation system developed as a part of the eXtreme Lateral Interbody Fusion (XLIF) system for lateral transpsoas interbody fusion, an alternative to anterior interbody fusion.

PURPOSE

To report two cases of atraumatic coronal plane vertebral body fractures in the early postoperative period after interbody fusion using XLIF cages, lateral plating using the XLP plate, and unilateral posterior pedicle screw instrumentation.

STUDY DESIGN

Case report. METHODS/SUMMARIES: Both patients were septuagenarian women with normal body mass indices and osteoporosis. The patients underwent L4-L5 XLIF with anterolateral instrumentation followed by posterior decompression and fusion using unilateral pedicle screws. In the early postoperative period (<or=6 weeks), the patients developed acute onset of severe low back pain without history of trauma. Imaging demonstrated coronal plane vertebral body fracture through the screw hole of the XLP plate in the superior vertebral body in one case and the inferior vertebral body in the other. One patient required kyphoplasty at the L4 level for pain relief. The other was treated conservatively. The nondisplaced fractures went on to union with pain resolution and successful fusion in both patients.

RESULTS

Coronal plane fractures occurred in 2 of 13 patients treated by the senior author using XLIF, the XLP plate, and unilateral pedicle screw instrumentation. Osteoporosis was likely a contributing factor in both patients. One potential mechanism for this unusual fracture pattern is subsidence of the cage with resultant cut-through of the fixed-angle screws through the osteoporotic vertebral body. Alternately, the fracture could have resulted from the stress riser created by the screw hole traversing an area of relative stress concentration directly adjacent to the cage.

CONCLUSION

Coronal plane vertebral fracture may occur in osteoporotic patients treated with XLIF and XLP lateral instrumentation. Unilateral pedicle screw instrumentation does not prevent this complication.

Radiographic and histopathologic analysis of osteolysis after total shoulder arthroplasty

HYPOTHESIS

This study analyzed clinical, radiographic, and histologic data from failed total shoulder arthroplasties (TSAs) to determine factors associated with osteolysis.

MATERIALS AND METHODS

From 1985 to 2005, 52 patients (mean age, 61.6 years) underwent revision TSA at a single institution at a mean of 4.3 years after their index surgery. Patients were retrospectively assigned to 2 cohorts based on the presence (n = 10) or absence (n = 42) of osteolysis around their implants on the last prerevision surgery radiographs. Clinical information, associated histopathology from tissues obtained at revision surgery, and polyethylene wear data from the retrieved glenoid components were compared between groups.

RESULTS

In the osteolysis group, 20% had screw fixation compared with 2.5% without osteolysis (P = .039). The radiolucency score was significantly higher in the osteolysis group: 12.7 +/- 2.0 vs 8.7 +/- 3.7 (P = .003). Wear analysis of the osteolysis group demonstrated significant increases in third-body particles compared with those implants without osteolysis (P = .004). Histology available from retrieved implants demonstrated particulate debris in 62% of patients with osteolytic lesions vs 67% without osteolytic lesions (P > .05).

DISCUSSION

Significant differences were found in patients with osteolytic lesions compared with patients undergoing TSA revision surgery without such lesions, specifically with regard to glenoids that used adjuvant screw fixation, the presence of increased radiolucent lines, and an abundance of third-body wear. No significant differences were found in particulate wear debris despite the prevailing notion that osteolysis is associated with particulate debris from implant wear.

CONCLUSION

Screw fixation and third-body wear were associated with osteolysis after TSA.

CT outperforms radiography for determination of acetabular cup version after THA

Precise evaluation of acetabular cup version is necessary for patients with recurrent hip dislocation after THA. We retrospectively studied 42 patients, who underwent THAs, with multiple cross-table lateral radiographs and CT scans to determine whether radiographic or CT measurement of acetabular component version is more accurate. One observer measured cup version on all radiographs. CT scans were interpreted by one observer. Twenty radiographs were measured twice each by two observers to determine intraobserver and interobserver reliability. We implanted cups in four model pelvises using navigation and compared measurements of anteversion made with radiographs and CT scans. Intraclass correlation coefficients (ICC) for anteversion measurements of two observers were 0.9990 and 0.9998, respectively, when comparing measurements of identical radiographs (intraobserver). Paired values for two observers measuring the same radiograph had an ICC of 0.9686 (interobserver) compared with 0.7412 for measurements from serial radiographs of the same component. The ICC comparing radiographic versus CT-based measurements was 0.6981. CT measurements had stronger correlations with navigated values than radiographic measurements. Accuracy of anteversion measurements on cross-table radiographs depends on radiographic technique and patient positioning whereas properly performed CT measurements are independent of patient position.

Comparison of early and delayed failed total shoulder arthroplasty

The purpose of the present study is to determine what factors contribute to early failure after total shoulder arthroplasty (TSA). Implants were retrieved from 69 patients after failed TSA and were retrospectively assigned to two cohorts based on time of failure: Early, less than 2 years (N = 34); and Delayed, longer than 2 years (N = 35). The clinical information, intraoperative information, most recent radiographs, and damage mapping were collected for all patients. Patients in the Early failure group were significantly older (63.9 +/- 9.5 years) than those in the Delayed group (49.9 +/- 12.8 years) by an average of 14 years. The proportion of osteoarthritis cases was significantly higher for the Early group compared to the Delayed group (62% vs. 40%). The Delayed group had higher damage scores for several damage modalities. Elderly age and osteoarthritis were significant factors that were associated with early failures after TSA.

Role of osteoblast-fibroblast interactions in the formation of the ligament-to-bone interface

The anterior cruciate ligament (ACL) inserts into bone through a characteristic fibrocartilagenous interface, which is essential for load transfer between soft and hard tissues. This multi-tissue interface is lost post ACL reconstruction, and the lack of an anatomic fibrocartilage interface between graft and bone remains the leading cause of graft failure. Currently, the mechanism of interface formation is not known. As a fibrocartilage-like tissue is found within the bone tunnel post ACL reconstruction, we hypothesize that fibroblast-osteoblast interactions at the graft-to-bone junction play a role in fibrocartilage formation. To test this hypothesis, a co-culture model permitting osteoblast-fibroblast communications was used to determine the effects of heterotypic interactions on cell phenotype and the development of fibrocartilage-relevant markers in vitro. It was found that co-culture decreased cell proliferation and osteoblast-mediated mineralization, while inducing fibroblast-mediated mineralization. Moreover, the expression of interface-relevant markers such as collagen type II and aggrecan were detected. Our findings suggest that osteoblast-fibroblast interactions may lead to cell trans-differentiation and eventual fibrocartilage formation. These results provide new insight into the mechanism of fibrocartilage formation, which are critical for interface tissue engineering and achieving biological fixation of soft tissue grafts to bone.