Diagnosis and Management of Pediatric Leg Length Discrepancy: Distal Femoral Physeal Bar & Genu Valgum Case Study

Patient Presentation and History

The patient is an 8-year-old male presenting with a 2-year history of progressive left lower limb shortening and a mild left knee valgus deformity. Parents initially noted a subtle limp at age 6, which has become more pronounced, particularly during sports activities. The child denies pain, neurological symptoms, or significant functional limitations beyond the altered gait pattern.

There is no reported history of significant trauma to the left lower extremity; however, a minor fall onto the left knee approximately 3 years prior was recalled by the parents, which did not result in immediate presentation to medical care. Past medical history is otherwise unremarkable. He was born full-term with no perinatal complications. There is no family history of known genetic syndromes, metabolic bone disorders, or significant orthopedic conditions. The patient is an active child involved in school sports.

The insidious onset of this deformity following a seemingly innocuous mechanism of injury is a classic presentation for an unrecognized pediatric physeal injury. In the pediatric population, the physes are the weakest biomechanical point in the musculoskeletal system, failing before the adjacent ligaments or diaphyseal bone. An unrecognized Salter-Harris fracture, particularly a compression-type injury (Salter-Harris Type V) or a minimally displaced fracture traversing the germinal layers, can lead to the formation of a transphyseal bony bridge, or physeal bar. This tethering effect halts longitudinal growth at the site of the bridge while the surrounding healthy physis continues to expand, inevitably resulting in angular deformity, limb length discrepancy, or a combination of both, depending on the anatomical location of the arrest.

Clinical Examination Findings

Inspection and Gait Analysis

On static standing examination, a noticeable pelvic obliquity was observed, with the left hemipelvis appearing lower. This was compensated by a mild left hip adduction and a compensatory equinus posture of the right ankle to achieve bilateral foot-flat stance. The left lower extremity exhibited apparent shortening. Mild genu valgum of the left knee was evident. Muscle bulk appeared symmetrical bilaterally. Skin integrity was uncompromised, with no obvious scars, erythema, or swelling.

Dynamic gait analysis revealed a pronounced short-leg gait characterized by lateral trunk lean over the left stance limb (compensated Trendelenburg gait) to minimize the joint reactive forces and reduce the moment arm of the body weight. During the swing phase of the right lower extremity, compensatory vaulting and slight hip circumduction were noted to allow for adequate foot clearance.

Palpation and Joint Assessment

Palpation along the entirety of the left lower extremity, including the hip, knee, and ankle joints, revealed no tenderness, warmth, or palpable masses. The distal femoral physis region of the left knee was non-tender to direct palpation. The medial and lateral collateral ligaments, as well as the patellar tendon, demonstrated normal tone and continuity. Joint effusions were absent bilaterally.

Range of Motion and Stability

• Hips: Full, pain-free range of motion bilaterally (flexion 130 degrees, extension 10 degrees, abduction 45 degrees, adduction 30 degrees, internal/external rotation 40/45 degrees).
• Knees: Full, pain-free range of motion bilaterally (flexion 140 degrees, extension 0 degrees). On stress testing, the left knee demonstrated mild valgus laxity (approximately 5 degrees compared to 0 degrees on the right) with a firm endpoint, indicative of pseudo-laxity secondary to the osseous valgus deformity rather than true medial collateral ligament incompetence.
• Ankles: Full, pain-free range of motion bilaterally (dorsiflexion 20 degrees, plantarflexion 50 degrees).

Leg Length Discrepancy Measurements

Standardized block testing was utilized to level the pelvis, which required a 3.5 cm block under the left foot to achieve horizontal alignment of the anterior superior iliac spines.
* True LLD: Measured from the Anterior Superior Iliac Spine to the medial malleolus, the left lower extremity was found to be 3.5 cm shorter than the right.
* Apparent LLD: Measured from the umbilicus to the medial malleolus, the left lower extremity was 4.0 cm shorter than the right, consistent with the true LLD and minimal fixed pelvic obliquity.
* Segmental Discrepancy:
* Left thigh length (greater trochanter to lateral femoral condyle): 2.0 cm shorter than the right.
* Left leg length (tibial plateau to medial malleolus): 1.5 cm shorter than the right.
* Circumferences: Thigh and calf circumferences were symmetrical, indicating no significant muscle atrophy or hypertrophy.

The presence of a segmental discrepancy involving both the femur and the tibia suggests either a dual-level injury from the initial trauma (e.g., a "bumper" type impact affecting both the distal femoral and proximal tibial physes) or a secondary growth suppression of the adjacent proximal tibial physis due to altered regional hemodynamics and abnormal mechanical loading across the knee joint over the preceding three years.

Neurological and Vascular Assessment

Motor strength was 5/5 in all major muscle groups of both lower extremities. Sensation was intact to light touch and pinprick in all dermatomes. Deep tendon reflexes (patellar and Achilles) were 2+ and symmetrical bilaterally. No pathological reflexes were elicited. Dorsalis pedis and posterior tibial pulses were palpable bilaterally and symmetrical. Capillary refill was brisk in all digits. No bruits were auscultated.

Spinal Alignment and Compensatory Mechanisms

Assessment of the spine revealed a non-structural, flexible lumbar scoliosis convex to the left during unsupported standing, which completely resolved upon leveling the pelvis with the 3.5 cm block. The Adam's forward bend test was negative for any fixed rotational prominence, confirming that the spinal curvature was purely compensatory to the pelvic obliquity induced by the leg length discrepancy.

Imaging and Diagnostics

Standard Radiographic Evaluation

• Standing AP Pelvis: Demonstrated pelvic obliquity with the left iliac crest positioned inferiorly, consistent with a left lower limb shortening. Bilateral hip joints appeared congruent with no signs of dysplasia or degenerative changes.
• Full Length Standing Teleoroentgenogram: This imaging modality is critical for precise quantification of the mechanical axis and segmental lengths. The left mechanical axis deviation was shifted into the lateral compartment of the knee, confirming a valgus malalignment. The Mechanical Lateral Distal Femoral Angle was measured at 81 degrees (normal 85 to 90 degrees), indicating a distal femoral valgus deformity. The Medial Proximal Tibial Angle was 86 degrees, which falls within the normal physiological range, isolating the primary angular deformity to the distal femur.
• Dedicated AP and Lateral Knee Radiographs: Visualized a focal area of sclerosis and premature physeal closure in the central-lateral aspect of the left distal femoral physis. The proximal tibial physis appeared undulating but without a distinct, radiographically visible osseous bridge, suggesting that the tibial shortening may be related to generalized limb hypoplasia or microvascular compromise rather than a discrete focal arrest.

Advanced Cross Sectional Imaging and Physeal Mapping

To accurately delineate the extent, location, and geometry of the physeal bar, advanced cross-sectional imaging is mandatory. Computed Tomography with fine contiguous cuts (1 mm) and multiplanar reconstructions can be utilized, but Magnetic Resonance Imaging is currently the gold standard due to its superior soft-tissue contrast and lack of ionizing radiation.

A dedicated physeal MRI protocol was ordered, utilizing 3D Spoiled Gradient-Recalled echo sequences and Fast Imaging Employing Steady-state Acquisition sequences with fat suppression. These sequences provide high-resolution differentiation between the high-signal unossified physeal cartilage and the low-signal osseous bridge.

The physeal mapping software was utilized to generate a three-dimensional topographical map of the distal femoral physis. The analysis revealed a discrete, continuous osseous bar located in the central-lateral quadrant of the distal femoral physis. The bar occupied approximately 25 percent of the total cross-sectional area of the physis. The surrounding physeal cartilage demonstrated normal signal intensity and thickness, indicating viable germinal matrix capable of resuming longitudinal growth if the tether is successfully resected.

Skeletal Age Assessment

Accurate determination of skeletal maturity is paramount for growth prediction and surgical timing. A left hand and wrist radiograph was obtained and compared against the Greulich and Pyle atlas. The patient's skeletal age was determined to be 8 years and 2 months, which closely correlates with his chronological age. Furthermore, the Sanders classification utilizing the hand radiograph placed him in Stage 1 (juvenile slow growth phase), indicating substantial remaining growth potential prior to the pubertal growth spurt.

Differential Diagnosis

When evaluating a pediatric patient with progressive leg length discrepancy and angular deformity, a comprehensive differential diagnosis must be considered to differentiate acquired physeal insults from congenital, metabolic, or infectious etiologies.

In this case, the localized nature of the deformity, the specific central-lateral tethering pattern on MRI, and the history of a fall strongly support the diagnosis of a post-traumatic physeal arrest resulting in a distal femoral physeal bar.

Surgical Decision Making and Classification

Classification of Physeal Bars

Physeal bars are generally classified based on their anatomical location, which dictates the resulting clinical deformity and the surgical approach required for resection. The most widely utilized anatomical classification includes:
1. Peripheral Bars: Located at the periphery of the physis. These typically cause progressive angular deformity with minimal initial leg length discrepancy, as the central physis continues to grow, creating a tethering effect.
2. Central Bars: Located within the central portion of the physis, surrounded by normal cartilage. These result in progressive leg length discrepancy and tenting or cupping of the metaphysis into the epiphysis, often without significant angular deformity.
3. Combined or Linear Bars: These span from the center to the periphery, resulting in a combination of profound length discrepancy and complex angular deformity.

Our patient presents with a central-lateral bar. The central component is responsible for the significant 3.5 cm leg length discrepancy, while the lateral extension acts as a tether against the growing medial physis, driving the progressive valgus deformity.

Growth Prediction and Deformity Analysis

To formulate a rational surgical plan, we must accurately predict the anticipated leg length discrepancy at skeletal maturity. The Paley Multiplier Method was utilized for this calculation.

For an 8-year-old boy, the lower extremity multiplier is approximately 1.4. The current discrepancy is 3.5 cm. If we assume complete cessation of growth in the left distal femur and proximal tibia (worst-case scenario without intervention), the discrepancy at maturity would be calculated by multiplying the current discrepancy by the multiplier, yielding a projected discrepancy of nearly 5.0 cm. However, because the normal right leg will continue to grow at a standard rate while the left leg's growth is severely blunted, the actual discrepancy at maturity would likely exceed 6 to 7 cm if left entirely untreated.

The distal femur contributes approximately 9 mm of longitudinal growth per year, and the proximal tibia contributes approximately 6 mm per year. Given that the patient has roughly 8 years of growth remaining until skeletal maturity (assuming cessation at age 16 for a male), the potential for massive discrepancy is immense.

Rationale for Operative Intervention

The decision to proceed with operative intervention is absolute in this scenario. The critical decision lies in selecting the appropriate surgical modality. The primary options include:
1. Physeal Bar Resection (Langenskiold Procedure): Indicated for bars occupying less than 50 percent of the physeal cross-sectional area in patients with at least 2 years of remaining growth.
2. Epiphysiodesis of the Contralateral Limb: Indicated for small predicted discrepancies (2 to 5 cm) at maturity, or in cases where bar resection is contraindicated (bar >50 percent, or near skeletal maturity).
3. Limb Lengthening: Indicated for discrepancies exceeding 5 cm, or when combined with acute deformity correction.

Given that the patient's bar occupies only 25 percent of the physis and he has substantial growth remaining, physeal bar resection is the primary indication to restore endogenous growth potential. However, bar resection alone will not acutely correct the existing 3.5 cm discrepancy, nor will it rapidly correct the established 5-degree valgus deformity.

Therefore, a comprehensive, staged surgical strategy is required:
1. Stage 1 (Current Intervention): Resection of the central-lateral distal femoral physeal bar with interposition grafting to restore longitudinal growth. Concurrently, application of a medial tension band plate (guided growth) to the distal femur to gradually correct the valgus deformity via hemiepiphysiodesis.
2. Stage 2 (Future Surveillance and Intervention): Close monitoring of longitudinal growth via semi-annual scanograms. If the bar resection successfully restores growth, the discrepancy may stabilize. If the 3.5 cm discrepancy persists and becomes symptomatic, a timed contralateral distal femoral epiphysiodesis can be performed closer to skeletal maturity, or an ipsilateral femoral lengthening can be considered if the patient refuses height reduction.

Surgical Technique and Intervention

Patient Positioning and Operating Room Setup

The patient was brought to the operating room and placed supine on a radiolucent Jackson table to facilitate unimpeded fluoroscopic imaging. General endotracheal anesthesia was administered. A non-sterile tourniquet was placed high on the left proximal thigh. The left lower extremity, from the toes to the groin, was meticulously prepped and draped in standard sterile orthopedic fashion. The ipsilateral gluteal fold was also prepped and draped into the sterile field to serve as the donor site for the autologous fat interposition graft.

A sterile bump was placed under the ipsilateral hip to prevent external rotation of the limb. Two C-arms were utilized, positioned to allow orthogonal views (Anteroposterior and Lateral) of the distal femur without requiring excessive movement of the extremity, thereby minimizing intraoperative delays during the critical mapping and resection phases.

Surgical Approach and Cortical Window Preparation

Given the central-lateral location of the physeal bar, a direct lateral approach to the distal femur was selected. A 5 cm longitudinal incision was made over the lateral aspect of the distal femur, centered over the metaphyseal-physeal junction. Dissection was carried sharply through the subcutaneous tissues. The iliotibial band was incised longitudinally in line with its fibers. The vastus lateralis was elevated anteriorly off the lateral intermuscular septum, exposing the lateral femoral metaphysis.

Meticulous hemostasis was achieved using electrocautery. The periosteum over the lateral metaphysis was incised and elevated, taking extreme care to preserve the perichondrial ring of LaCroix and the peripheral aspect of the physis.

Under direct fluoroscopic guidance, a rectangular cortical window (approximately 1.5 cm by 1.5 cm) was outlined on the lateral metaphysis, positioned 1 cm proximal to the radiolucent physeal line. Multiple drill holes were created along the perimeter of the planned window using a 3.2 mm drill bit. A sharp osteotome was then used to connect the drill holes, and the cortical window was carefully elevated and preserved in a saline-soaked sponge for later replacement.

Physeal Bar Resection and Endoscopic Visualization

With the metaphyseal cancellous bone exposed, a high-speed motorized burr (starting with a 4 mm cutting burr and transitioning to a diamond burr) was introduced through the window. The trajectory of the burr was strictly guided by the preoperative MRI map and continuous multiplanar fluoroscopy.

The metaphyseal bone was systematically excavated toward the central-lateral quadrant. The transition from normal cancellous bone to the dense, sclerotic bone of the physeal bar was tactilely distinct. The bar was meticulously burred away. As the resection progressed distally, the appearance of normal, pearlescent blue-white physeal cartilage indicated the successful removal of the osseous tether.

To ensure absolute completeness of the resection, a 30-degree, 2.7 mm arthroscope was introduced into the metaphyseal cavity. Endoscopic visualization is a critical adjunct, allowing direct inspection of the resection cavity margins. The cavity was thoroughly irrigated, and the arthroscope confirmed a continuous rim of healthy, unossified physeal cartilage surrounding the resection bed, extending down to the epiphyseal bone. No residual osseous bridging was visualized.

Interposition Graft Placement

To prevent the recurrence of the physeal bar, the resection cavity must be completely filled with an inert interposition material that mechanically blocks osteogenic migration while allowing continued expansion of the surrounding physis. Autologous fat is the preferred biological material due to its lack of immunogenicity, pliability, and proven efficacy in preventing re-ossification.

Attention was turned to the prepped ipsilateral gluteal fold. A small transverse incision was made, and a generous block of subcutaneous adipose tissue was harvested. The donor site was irrigated and closed in layers.

The harvested fat graft was fashioned into appropriate dimensions and packed tightly into the metaphyseal resection cavity. It is imperative that the fat graft completely fills the void and is under slight pressure to prevent hematoma formation, which could serve as a scaffold for recurrent bone formation. The previously elevated cortical bone window was then replaced over the defect. To prevent extrusion of the fat graft, the cortical window was secured using a low-profile titanium micro-plate and two unicortical screws.

Guided Growth Application for Genu Valgum

Following the successful resection of the physeal bar, attention was directed toward addressing the 5-degree valgus deformity. A medial hemiepiphysiodesis utilizing a tension band construct was planned.

A 3 cm longitudinal incision was made over the medial aspect of the distal femur, centered over the physis under fluoroscopic guidance. The subcutaneous tissues were dissected, and the medial retinaculum was incised to expose the medial femoral condyle and metaphysis. A Keith needle was inserted into the mid-substance of the medial physis to serve as a trajectory guide.

A two-hole, non-locking titanium tension band plate (8-plate construct) was selected. The plate was positioned centrally over the medial physis, ensuring that the central hole aligned perfectly with the Keith needle. Guide wires were inserted through the proximal and distal holes of the plate into the metaphysis and epiphysis, respectively. Fluoroscopy in both AP and lateral planes confirmed optimal central placement, avoiding the intra-articular space and ensuring the screws were parallel to the joint line.

Cannulated, self-tapping 4.5 mm titanium screws were then advanced over the guide wires. The screws were intentionally left slightly proud of the plate to facilitate future removal once the angular deformity is corrected. The surgical sites were thoroughly irrigated, and the incisions were closed in a layered fashion using absorbable sutures for the deep fascia and subcutaneous tissues, followed by a subcuticular closure for the skin. Sterile dressings and a knee immobilizer were applied.

Post Operative Protocol and Rehabilitation

Immediate Postoperative Phase

The patient was admitted for 24-hour observation and intravenous pain management. Prophylactic intravenous antibiotics (Cefazolin) were administered for 24 hours postoperatively.

Due to the creation of the lateral metaphyseal window, the distal femur is structurally compromised, placing the patient at an increased risk for a pathological fracture through the stress riser. Therefore, the patient was placed in a hinged knee brace locked in extension and instructed to remain strictly non-weight-bearing on the left lower extremity for the first four weeks.

Physical therapy was initiated on postoperative day one, focusing on gentle, passive, and active-assisted range of motion exercises for the hip, knee, and ankle to prevent arthrofibrosis and maintain joint mobility. Cryotherapy and elevation were heavily emphasized to manage postoperative edema.

Intermediate Rehabilitation and Growth Monitoring

At the four-week postoperative mark, standard radiographs were obtained to confirm the maintenance of hardware position and the absence of metaphyseal fracture. Upon confirmation of stable osseous architecture, the patient was transitioned to partial weight-bearing (50 percent) for an additional two weeks, followed by progression to full weight-bearing as tolerated.

The hinged knee brace was unlocked to allow full range of motion during ambulation. Physical therapy was advanced to include closed kinetic chain exercises, proprioceptive training, and progressive resistance exercises focusing on quadriceps and hamstring strengthening to counteract any disuse atrophy.

Long Term Surveillance and Secondary Interventions

The long-term success of this procedure hinges on meticulous radiographic surveillance. The patient is scheduled for clinical evaluation and full-length standing teleoroentgenograms every six months.

The primary objectives of these follow-up visits are twofold:
1. Monitor Valgus Correction: The medial tension band plate will gradually tether the medial physis, allowing the lateral physis (now freed from its osseous bar) to grow and correct the valgus deformity. Once the mechanical axis is restored to neutral, the tension band plate and screws must be promptly removed to prevent overcorrection into varus.
2. Assess Longitudinal Growth: The progression of the leg length discrepancy must be tracked. If the bar resection is successful, the velocity of longitudinal growth in the left femur should normalize, and the discrepancy should remain static at 3.5 cm or potentially improve slightly. If the discrepancy continues to increase, it indicates a failure of the bar resection and recurrence of the physeal tether.

Given the existing 3.5 cm discrepancy, it is highly probable that the patient will require a secondary intervention as he approaches skeletal maturity. Based on the multiplier method predictions, a carefully timed percutaneous epiphysiodesis of the right distal femur and proximal tibia may