Thigh and Knee — Surgical Anatomy, Approaches, and Arthroscopy

Introduction

The thigh and knee region contains the longest bone in the body (femur), the largest joint (knee), and a substantial muscular envelope that organizes the major movements of the lower extremity. The surgical approaches to this region are diverse: the thigh compartments require specific fasciotomy approaches; the distal femur and proximal tibia require approaches tailored to the location of pathology (lateral, medial, anterior); and the knee joint can be accessed through the standard medial parapatellar approach, the muscle-sparing variants (midvastus, subvastus), and the dedicated arthroscopic portals. The knowledge of these approaches, of the muscular compartments of the thigh, of the neurovascular structures (femoral nerve and vessels anteriorly, sciatic nerve posteriorly, popliteal vessels in the popliteal fossa), and of the arthroscopic portals and intra-articular anatomy is essential to the orthopedic surgeon. This chapter draws on Orthopaedic Surgical Approaches, Netter’s Concise Orthopaedic Anatomy, and Gray’s Anatomy.

Thigh Anatomy and Compartments

The thigh has three principal muscular compartments separated by intermuscular septa attached to the linea aspera of the femur: Anterior compartment: Contains the quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius), the sartorius, the iliacus and psoas (proximally), and the pectineus. Innervated principally by the femoral nerve (L2-L4). Functions principally as knee extension and hip flexion. Medial compartment: Contains the adductor longus, brevis, and magnus; the gracilis; the obturator externus. Innervated principally by the obturator nerve (L2-L4). Functions as hip adduction. Posterior compartment: Contains the hamstrings (biceps femoris with long and short heads, semitendinosus, semimembranosus). Innervated by the sciatic nerve (tibial portion for most; common peroneal portion for the short head of biceps). Functions as hip extension and knee flexion. The principal landmarks and neurovascular structures include: Femoral triangle: Bounded by the inguinal ligament superiorly, the sartorius laterally, and the adductor longus medially. Contains the femoral artery (laterally to medially: NAVEL — Nerve, Artery, Vein, Empty space, Lymphatic). Adductor canal (Hunter’s canal): A tunnel in the middle third of the thigh through which the femoral vessels pass deep to the sartorius. The artery becomes the popliteal artery as it emerges through the adductor hiatus into the popliteal fossa.

Popliteal fossa: The posterior knee region bounded by the biceps femoris (superolateral), the semimembranosus/semitendinosus (superomedial), and the two heads of gastrocnemius (inferiorly). Contains the popliteal artery, popliteal vein, and tibial/common peroneal nerves (the sciatic nerve divides at the apex of the fossa).

Approaches to the Femoral Shaft

The femoral shaft is approached for fracture fixation, tumor resection, and biopsy. The principal options: Anterolateral approach to the femur: Standard for plate fixation. Develops the interval between the vastus lateralis and the rectus femoris, with the rectus retracted medially. Provides good exposure with limited disruption of the principal blood supply. Posterolateral approach: Through the interval between the iliotibial band and the biceps femoris, providing posterolateral access to the femur. Used for plate fixation of distal femoral fractures (Topic Trauma-24). Posterior approach: Less commonly used; develops the interval between the medial and lateral hamstrings, with attention to the sciatic nerve. Provides access to the posterior femur. Antegrade and retrograde nailing entry: As described in Topic Trauma-23, antegrade nailing uses a piriformis or trochanteric entry, and retrograde nailing uses an intercondylar notch entry through a small parapatellar arthrotomy.

Knee Bony and Articular Anatomy

The knee joint comprises: Tibiofemoral joint: Hinge joint between the distal femur (medial and lateral condyles) and the proximal tibia (medial and lateral plateaus). Patellofemoral joint: Between the patella and the trochlear groove of the distal femur. Proximal tibiofibular joint: Synovial joint between the lateral tibial condyle and the fibular head. The cruciate ligaments (ACL, PCL) lie within the joint, addressed in Topic Trauma-26. The menisci (medial and lateral) are fibrocartilaginous structures providing load distribution and joint conformity. The collateral ligaments (MCL medially, LCL with the posterolateral corner laterally) provide coronal-plane stability.

Knee Approaches

Medial Parapatellar Approach The medial parapatellar approach is the classical and most commonly used approach for total knee arthroplasty, knee arthrotomy, and many open knee procedures. The approach uses a longitudinal anterior midline skin incision, with the deep arthrotomy beginning at the medial border of the quadriceps tendon, extending distally along the medial border of the patella, and continuing distally along the medial border of the patellar tendon. The quadriceps tendon is incised approximately 1 to 2 cm medial to the patella to leave a cuff for closure. The patella is then everted (or simply translated) laterally to expose the joint. The approach provides excellent visualization of the entire joint but disrupts the vastus medialis insertion on the patella, with consequent quadriceps weakness in the short term and contribution to extensor mechanism imbalance. The medial patellofemoral ligament (MPFL) is partially disturbed, and may contribute to lateral subluxation if not properly reconstructed. Midvastus Approach The midvastus approach preserves a larger portion of the vastus medialis by splitting the muscle in line with its fibers rather than detaching its insertion on the patella. The approach develops a muscle-splitting plane through the vastus medialis obliquus (VMO) from the medial border of the patella for approximately 4 to 5 cm proximally. The approach provides similar exposure to the medial parapatellar with theoretical preservation of extensor mechanism integrity. Subvastus Approach The subvastus approach preserves the entire vastus medialis by elevating the muscle from the medial femur (rather than splitting it) and reflecting it laterally. The approach provides the greatest preservation of extensor mechanism but requires significant elevation of the muscle and has more limited exposure of the lateral compartment. Lateral Parapatellar Approach The lateral parapatellar approach is the mirror image of the medial parapatellar but is less commonly used. It is reserved for specific indications (severe valgus deformity where the medial structures must be approached from outside-in, lateral patellar instability surgery). Posterior Approach (Burks-Schaffer Modification of Henderson) The posterior approach to the knee uses an S-shaped or hockey-stick incision in the popliteal fossa. The approach is used for PCL tibial inlay reconstruction, posterior tibial plateau fixation, posterior capsular procedures, and exploration of the popliteal vessels and tibial nerve. The medial head of the gastrocnemius is retracted laterally to expose the posterior tibia. The popliteal vessels and tibial nerve are identified and protected.

Specific Approaches for Tibial Plateau Fractures

For lateral tibial plateau fractures (Schatzker I, II, III), the approach is typically through an anterolateral incision with a submeniscal arthrotomy to allow direct visualization of the articular surface (Topic Trauma-25). For medial tibial plateau fractures (Schatzker IV), a medial approach is used. For bicondylar fractures (Schatzker V, VI), dual approaches (medial and lateral) with separate incisions are preferred to avoid the central anterior incision and the associated soft-tissue compromise.

Knee Arthroscopy

Knee arthroscopy is one of the most commonly performed orthopedic procedures, with portals as detailed in Topic Trauma-26. The standard anterolateral and anteromedial portals provide access to the entire joint. The arthroscopic examination systematically visualizes the suprapatellar pouch, the patellofemoral joint, the medial and lateral gutters, the medial and lateral compartments (menisci and articular surfaces), the intercondylar notch (ACL, PCL), and the posteromedial and posterolateral compartments. The arthroscopic procedures include meniscectomy, meniscal repair, cartilage procedures (microfracture, OATS, ACI), ACL reconstruction, PCL reconstruction, loose body removal, and synovectomy.

Compartment Syndrome of the Thigh and Knee

Thigh compartment syndrome is uncommon but described, particularly with high-energy crush injuries, vascular injury with reperfusion, prolonged operative positioning, and anticoagulation-related hematomas. Fasciotomy of the thigh uses two longitudinal incisions — lateral and medial — providing release of the anterior compartment (lateral incision), the posterior compartment (lateral or separate posterior incision), and the medial compartment (medial incision).

Neurovascular Anatomy of the Thigh and Knee

The principal neurovascular concerns include: Femoral nerve: Descends through the femoral triangle. Vulnerable in retroperitoneal injuries and during anterior approaches. Femoral artery and vein: Pass through the femoral triangle, then through the adductor canal to become the popliteal vessels. Saphenous nerve: Branches from the femoral nerve in the femoral triangle, accompanies the femoral artery through the adductor canal, and emerges from the canal to descend along the medial side of the leg. Provides sensation to the medial leg. Sciatic nerve: Divides into tibial and common peroneal divisions at the apex of the popliteal fossa.

Common peroneal nerve: Continues laterally to wrap around the fibular neck (vulnerable to injury here — Topic Trauma-31). Tibial nerve: Continues distally through the popliteal fossa. Popliteal artery and vein: Pass through the popliteal fossa. Vulnerable in knee dislocations (Topic Trauma-26) and distal femur/proximal tibia fractures.

Summary and Take-Home Points

The thigh has three principal compartments (anterior with quadriceps and femoral nerve, medial with adductors and obturator nerve, posterior with hamstrings and sciatic nerve), with the femoral triangle at the proximal end and the popliteal fossa at the distal end as the principal neurovascular landmarks. The femoral shaft is approached for fracture fixation typically through an anterolateral approach between vastus lateralis and rectus femoris. The knee joint is accessed through the medial parapatellar approach (the workhorse for TKA and major knee procedures), with muscle-preserving variants (midvastus, subvastus) gaining popularity for selected indications. The lateral parapatellar approach is reserved for severe valgus or lateral instability. The posterior approach is used for posterior tibial plateau fractures, PCL tibial inlay, and exploration of the popliteal vessels. Knee arthroscopy through standard anterolateral and anteromedial portals provides access to the entire joint for meniscal, cartilage, ligament, and synovial procedures. The principal neurovascular structures of the popliteal fossa (popliteal vessels, tibial and common peroneal nerves) are the critical considerations in posterior knee and proximal tibia procedures. The common peroneal nerve around the fibular neck is vulnerable to direct injury in lateral approaches and to traction injury in knee dislocations. The chapter that follows turns to the lower leg, completing the proximal-to-distal lower extremity sequence.