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SURGICAL APPROACHES: LATERAL APPROACH IN TKA
BONE DEFORMITIES (DEVELOPMENTAL) - (FIGURES 1 & 2)
LATERAL APPROACH - RATIONALE
STEP I: I-T BAND RELEASE/LENGTHENING
STEP II: LATERAL ARTHROTOMY -CORONAL Z-PLASTY
STEP III: PATELLA DISLOCATION - JOINT EXPOSURE
STEP IV: TIBIAL SLEEVE RELEASE - OSTEOPERIOSTEAL
STEP V: FEMORAL SLEEVE RELEASE - OSTEOPERIOSTEAL
INSTRUMENTATION - BONE RESECTIONS
STEP VI: SOFT TISSUE (PROSTHETIC JOINT) CLOSURE
Summary - Conclusions
Associate Professor of Clinical Orthopaedics
Pennsylvania State University College of Medicine
Chief, Division of Orthopaedic Surgery
Lehigh Valley Hospital
PATHOLOGIC ANATOMY - VALGUS KNEE
Fixed valgus deformity is usually associated with external tibial rotation. The deformity is prevalent in females (9:1), and rheumatoid arthritis is an underlying disease in a higher number of cases as compared to the more common osteoarthritic knee.
The fascia lata extension envelops the quadriceps with attachment to the posterior aspect of the femur. The distal lateral confluence becomes the iliotibial (I-T) band with distinct insertion into Gerdy's tubercle and the lateral tibial plateau. Transverse and oblique fibers extend to the patellar mechanism. This distinct layer is referred to as the lateral retinaculum 6. The fascia attaches to bone via Sharpey's fibers and into the myofascia of the anterior compartment of the calf.
The I-T band and the lateral retinaculum are, by definition, deforming factors in the fixed valgus knee. The I-T band attachment to the upper tibia produces a valgus moment with external rotation. The lateral retinaculum (oblique and transverse extensions) produces a lateral (subluxing) moment to the patellar mechanism. The lateral retinaculum is a distinct layer from the deeper capsular/fat pad and vastus lateralis attachments.
The extra-articular layer also includes the lateral hamstring (biceps femoris), the fabellofibular ligament,7, 8 the lateral head of the gastrocnemius, and the popliteus muscle, which becomes an intra-articular tendon insertion. These structures may be contracted secondary to the long-standing valgus, especially in rheumatoid or inflammatory conditions with myofibrosis. Bony deformity (hereditary, acquired, or posttraumatic) further increases the contractures.
The lateral superficial layer differs from the (compliant) medial oblique retinaculum of the vastus medialis in that the lateral retinaculum is relatively noncompliant. This noncompliant lateral fascial extension to the patellar mechanism, coupled with contractures of the deeper layer, becomes a major determinant of the soft tissue deformity in the valgus knee.
INTRA-ARTICULAR (DEEP LAYER-FIGURE 3)
The deep anterior and posterior lateral soft tissue layers are contracted to different degrees, depending on factors such as the underlying pathology, longevity of the deformity, bony pathology, and others. Management of this deep layer in valgus TKA represents the key to correction of the tibial rotation and centralization of the patella following prosthetic insertion.
BONE DEFORMITIES (DEVELOPMENTAL) - (FIGURES 1 & 2)
The lateral femoral condyle is smaller and eroded secondary to arthritic changes. Peripheral osteophytes and intercondylar notch stenosis are common. The anatomic femoral axis is significantly increased.
The tibia is externally rotated, and the tibial tubercle is positioned laterally. The lateral plateau has varying degrees of central bone resorption and peripheral osteophyte encroachment.
The patella is often subluxed laterally. The lateral facet is frequently deformed (flattened or concave), with large traction osteophytes secondary to lateral overpull. Patella alta, with an expanded suprapatellar pouch, is common. The suprapatellar soft tissue is hypertrophied.
Bone deformities secondary to the lateral femoral condyle or tibial plateau fractures may contribute to or accentuate pre-existing valgus. If the deformity is minor and/or correctable and limited to the lateral compartment, supracondylar varus osteotomy or lateral unicompartment replacement is an option to TKA. In either case, the direct lateral approach enhances exposure and provides other advantages that will be discussed in the technique section.
The standard medial parapatellar approach is the most commonly utilized procedure for all total knees.9-12 The subvastus and, more recently, the midvastus13 variations have been described. There is a general consensus that sequential releases should be performed from the femoral side prior to instrumentation in fixed valgus.14-17 Releases include the posterolateral complex, the posterior cruciate ligament (PCL), and the I-T band. In extremely severe deformities, lengthening of the lateral hamstring and/or lateral gastrocnemius, with or without resection of the fibular head, can be performed. A second posterolateral incision may be required. However, inside-out releases are the norm, without consideration of joint seal.
The medial approach in valgus TKA fails to address the pathologic anatomy rationally and biomechanically. Patellar maltracking is more common, and there is increased potential for inaccurate flexion-extension gap balancing and less than optimum femorotibial stability. Technical disadvantages of the approach include: (1) it is indirect; (2) it increases external rotation of the tibia; (3) access to the posterolateral corner is more difficult; (4) an extensive lateral release is still required; (5) joint seal and prosthetic soft tissue coverage is difficult if not impossible; (6) vascularity to the quadriceps patella tendon (QPT) mechanism and lateral skin (beneath the extensive lateral release) is decreased;18 (7) it does not allow for correction of the external rotation contracture of the tibia; and (8) it may encourage overreleasing of deep soft tissues.
LATERAL APPROACH - RATIONALE
The lateral approach in valgus deformity, by contrast, addresses the pathologic anatomy in a rational and sequential manner.3,4,19-21 The approach (1) is direct, (2) accomplishes the extensive "lateral release" with the exposure, (3) decreases skin undermining, (4) internally rotates the tibia with improved access to the pathologic posterolateral corner, (5) allows for better titration of sequential releases based on flexion-extension gap balance requirements, (6) preserves vascularity because the medial side is untouched,18 (7) allows for planned soft tissue gap and prosthetic coverage, (8) centralizes the QPT mechanism which optimizes patella tracking, (9) improves femorotibial alignment stability, and (10) rehabilitation is unimpeded because the medial quadriceps remains intact.
The surgical technique of the direct lateral approach differs substantially from the standard medial parapatellar approach. The surgeon is less familiar with the lateral side of the knee; orientation is reversed, and a more careful handling of the soft tissues is required.
The recommended skin incision in the virgin knee follows the Q-angle and is slightly lateral to the patella, lateral border of the patellar tendon, and the tibial tubercle (Figure 4). Long incisions are preferred, especially in large knees. It is important to avoid unnecessary undermining. In previously operated knees, the existing incision should be incorporated and extended proximally and distally. If multiple incisions are present, select the most direct or the latest operated tract.
STEP I: I-T BAND RELEASE/LENGTHENING (FIGURE 5)
Proximal I-T band exposure is gained by freeing and retracting the vastus lateralis from the fascial envelope to expose the posterior femur. The broad fascial band is released from the femoral attachment and stripped proximally and distally to the condylar attachments. Dissection is initiated with a hemostat and completed with a finger or blunt instrument. Following exposure and longitudinal stripping from the femur, a varus moment is placed at the knee joint, bow-stringing the I-T band. The "pie crust" lengthening, as used in percutaneous Achilles tendon lengthening, is preferred because it allows the fascia to remain in continuity. However, transverse, Z-plasty, or V-Y techniques can also be utilized.10,14 The lengthening is performed from inside-out, taking care not to undermine the subcutaneous layer. The peroneal nerve can be exposed as needed in severe cases.
Initial correction of 10° to 15° can be accomplished by this lengthening technique. The proximal relaxation allows for more precise or titrated release at the joint level. In moderate cases, sleeve releases of the tibia and/or femur may not be required if the intra-articular pathology is primarily bone loss. If the deformity is mild or totally correctable under anesthesia, Step I can be eliminated.
STEP II: LATERAL ARTHROTOMY -CORONAL Z-PLASTY (FIGURES 6 AND 7)
The lateral arthrotomy incision separates the superficial from the deep layers via a coronal plane Z-plasty technique. The proximal, middle, and distal segments require different anatomic dissection techniques. The superficial or first layer incision extends proximally from the lateral border of the rectus femoris to, but not through, the musculotendinous junction of the vastus lateralis (V-L); in the midsegment, it proceeds laterally 2 to 4 cm from the patella border, and distally through the anteromedial aspect of Gerdy's tubercle and the anterior compartment fascia.
Proximally, the incision extends from superficial lateral to deep medial, entering the suprapatellar pouch at an estimated 45° angle. The laminations of the central quadriceps tendon allow for a natural plane dissection to the proximal or musculotendinous junction of the V-L. The V-L tendon inserts at the proximal lateral patella. The tendon is substantially thick (6 to 10 mm), which allows for a relaxation (coronal plane Z-plasty) approach. The incision continues from the musculotendinous junction superficially, through 50% of the tendon, ending at the patella. Finger tension from the undersurface of the patella and V-L tendon allows for a controlled (sharp knife) coronal plane dissection (Figure 7). The deep (50%) fibers are detached from the patella rim, maintaining the lateral sleeve. Plicae bands are sectioned medially in order to enhance the soft tissue gap closure. The distal aspect of the V-L insertion blends into the lateral capsular attachment and becomes more compliant after the proximal dissection has been completed.
The fat pad is incised obliquely to include the lateral meniscus, preserving approximately 70% of the fat pad with the meniscus and 30% with the patellar tendon (Figure 8). Lateral fat pad mobilization and preservation can vary according to soft tissue defects and surgeon preference. The lateral inferior geniculate artery provides excellent vascularization. The fat pad incision can be made prior to or as the patella is being everted. The advantage of incising with patella eversion is that soft tissue tension is increased and a more definite incision path is defined. The lateral fat pad-meniscal sleeve can be mobilized and expanded for soft tissue closure in very severe cases.
The distal extension of the retinacular incision splits the medial aspect of Gerdy's tubercle and continues distally into the anterior compartment fascia. Osteoperiosteal elevation (using a sharp osteotome) beginning at mid-Gerdy's to, but not including, the tibial tubercle protects the patellar tendon attachment (Figure 8). Including the medial fibers of the anterior tibial muscle maintains continuity of the sleeve and allows for safer dislocation of the patellar mechanism. The medial sleeve broadens the effective width of the patellar tendon attachment by 2 to 3 cm; it protects the insertion of the patellar tendon and enhances the internal rotation moment of the tibia. Care must be taken to control (cauterize) or avoid the recurrent branch of the anterior tibial artery. The patella is now prepared for translocation and/or eversion.
The lateral approach preserves the surgical option of formal tibial tubercle osteotomy, preferred by some surgeons and reported in the literature16,17,22 via the medial approach. Performing the osteotomy from lateral to medial (with the extended sleeve) is more anatomical and maintains other benefits of the direct lateral approach. Personal experience has shown that formal tubercle osteotomy is rarely required if the osteoperiosteal technique is mastered. A proximal soft tissue incision, including a lateral to medial rectus snip, is helpful to enhance exposure and is preferred over formal tibial tubercle osteotomy.
STEP III: PATELLA DISLOCATION - JOINT EXPOSURE (FIGURE 9)
The medial-posterior corner is the most difficult exposure with the lateral approach. Soft tissue elevation from the upper medial tibial plateau is best accomplished with electrocautery. The medial meniscal rim is preserved. A Homan-type retractor placed through or inside the meniscal rim and behind the posterior medial tibial plateau levers the tibia forward. The cruciate attachments and capsule may be released from the posterior femur at this time or following tibial sleeve release (Step IV).
STEP IV: TIBIAL SLEEVE RELEASE - OSTEOPERIOSTEAL (FIGURE 10)
In extreme cases, the dissection is extended to the proximal fibula, which can be resected from inside to the outer cortex. This technique preserves the attachments of the LCL and biceps femoris and decompresses the peroneal nerve as it passes around the upper fibula.
Direct visualization, with the tibia internally rotated, ensures that safe, sequential or titrated releases are performed. The knee should be extended and flexed following tibial sleeve release to evaluate correction (Figure 11). Use of lamina spreaders aids in assessment. If there is an obvious nced for femoral sleeve release, proceed to the next stop. If gaps have been corrected to a reasonable mechanical axis, proceed to bone resections and fine-tune with trial components.
STEP V: FEMORAL SLEEVE RELEASE - OSTEOPERIOSTEAL (FIGURE 12) Figure 12: Step V: Femoral Sleeve Release. Osteoperiosteal release begins under the popliteus insertion and extends proximally as illustrated.
Figure 12: Step V: Femoral Sleeve Release. Osteoperiosteal release begins under the popliteus insertion and extends proximally as illustrated.
The femoral attachment of the popliteus, LCL, and posterolateral capsular attachments must be released in severe and some moderate deformities. Technically, a subperiosteal release with a sharp osteotome is preferred. The osteotome is placed beneath the periosteum of the popliteus insertion and continues proximally. The LCL and posterior capsular complex structures are included. In moderate deformities, selected or titrated releases are preferable and best performed at the time of flexion-extension gap evaluation (spacer blocks or tensors) and/or at the time of trial reduction (Figures 11 ,13, and 14).
INSTRUMENTATION - BONE RESECTIONS (FIGURES 13 & 14)
The recommended resection of the proximal tibia is perpendicular to the mechanical (anatomical) axis with a 7° to 10° posterior inclination. Proper rotational orientation (proximal tibia to ankle or foot), therefore, is critical because curvatures in one plane can affect angulation in another plane. Failure to correct the external tibial rotation may influence the plane of resection. The medial approach in valgus TKA increases external rotation of the tibia, whereas the direct lateral approach internally rotates the tibia, allowing for better assessment of anatomical landmarks, depth, and plane of resection.
The depth of tibial resection follows normal guidelines. The lesser involved medial plateau should dictate the depth of resection. Minimal lateral resection is the norm. Grafting (or shimming) of the lateral tibial plateau is preferable (within reason) to deeper resections because the depth of resection will affect flexion gap stability, joint line, and patella position.
The femoral resection may be influenced by the distorted anatomy. The prominent medial and pathologic lateral compartment may skew the instrumentation (intra or extramedullary). Minimal to no resection of the lateral distal and posterior femoral condyle is the norm in severe deformity.
Rotational resections are based on various landmarks with different instrument systems.15,16,23,24 Systems based on the posterior femoral condyles produce an internally positioned femoral component, much exaggerated in the valgus knee. Systems based on the transepicondylar axis25 or the tibial axis (and flexion tension)3,19,24 more accurately position the femur for the rotational (coronal plane) resection and a balanced flexion gap. Patellar tracking is critically dependent on proper femoral rotation alignment, in addition to soPt tissue balancing and a proper (anatomic) femoral prosthetic component.
The distal femoral resection plane recommended is 4° to 5° valgus, and the depth of resection is based on extension gap requirements (instrument systems dependent). The goal is to mate the extension gap to a stable flexion gap. Fine-tuning is accomplished with spacers (Figure 13) or at the time of trial reduction (Figure 14). Trial reduction allows for assessment of stability and mobility at the femorotibial and patellofemoral joints. Note the natural patella tracking, tibial tubercle position, and stable flexion at 130° in the clinical case following LCS rotating plattorm insertion (Figure 14). External tibial rotation has been correctod, and the (untouched) medial forces now balance the soft tissues through the flexion-extension arc of motion.
The direct lateral approach best prepares and exposes the distal femur and proximal tibia for the critical axial and rotational cuts. The advantages citod will decrease the potential for malresections and will allow for better assessment of stability in all planes (varus-valgus, rotation, anteroposterior, patellofemoral). The need for medial ligament advancement is eliminated as the soft tissues realign with correction of mechanical axis.
STEP VI: SOFT TISSUE (PROSTHETIC JOINT) CLOSURE (FIGURE 15)
Soft tissue closure is completed with the knee flexed. The expanded lateral soft tissue sleeve (coronal Z-plasty) is positioned to the medial sleeve. Towel clips or stay sutures are utilized, and the knee is extended and flexed through the maximum range. Distal to proximal closure is recommended.
Distally, anatomic reattachment of the I-T band and posterolateral sleeve to Gerdy's tubercle and the medial sleeve stabilizes the posterolateral corner. In the midsegment, the capsule is sutured to the lateral border of the retinaculum. Proximally, the vastus lateralis tendor is reattached in the expanded (coronal plane Z-plasty) position with the knee in maximal flexion. The knee is ranged to a full flexion position (140-150°), and soft tissue compliance and integrity of the joint seal are checked. Appropriate adjustments or reinforcing sutures can be implemented at this time. The preoperative noncompliant-deforming lateral soft tissue structures are now more compliant and allow for coverage of the prosthetic joint.
The medial approach is the recommended surgical approach in all standard textbooks relating to TKA, including correction of fixed valgus deformity.9,11,26,27 Technique points stressed are sequential release of extra- and intra-articular soft tissue contractures from the femoral side. Insall10 stressed the importance of proximal I-T band release. Ranawat14 and others1,15-17 stress the need for an extensive lateral retinacular release (with coagulation of the lateral geniculate vessels), proximal release of the I-T band, and cautery release of the posterolateral (arcuate) complex from the femur in valgus deformities over 15° (moderate) and over 30° (severe). Release or lengthening of the lateral gastrocnemius and lateral hamstring is recommended if the above steps are not adequate. Hungerford and associates16 categorized fixed-valgus deformity into two types based on medial soft tissue integrity. Type I includes intact medial stabilizers, and Type II has attennated medial stabilizers. Type II (severe) deformities are treated with medial soft tissue advancement, a stop most surgeons prefer to avoid. If flexion-extension or mediolateral balancing is unsatisfactory, they recommend use of a more stable prosthesis.
The direct lateral approach best addresses the technical challenges of fixed valgus and provides the surgeon with a surgical option to the standard medial approach. Cameron and colleagues28 discussed the lateral approach in TKA as an option but did not describe specifics of the technique. Buechel21 described a sequential three-step lateral release via the lateral approach, a slight variation of the technique described herein. This author's initial clinical experience and technical steps3 were described in 19854 with early follow-up results reported in 1991.
The technical steps described have been refined from the original description and are available for viewing on videotext.20 Significant changes include
These refinements in technique have improved the understanding of the anatomical correction and have decreased the learning curve for the approach. The approach requires an appreciation of the lateral soft tissue structures of the knee and is more technically demanding. Patellar eversion and orientation are reversed, and instrumentation and tibial exposure (posteromedial) are somewhat more difficult. However, clinical results3,21 of the direct lateral approach in valgus TKA have eliminated patellar maltracking and have improved alignment stability--the basic goals of TKA (Figure 16).
Summary - Conclusions
Maîtrise Orthopédique n° 96 - August 2000
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