The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 89, Issue 4

Scientific Articles | April 01, 2007

The Anatomy of the Posterior Aspect of the Knee: An Anatomic Study

Robert F. LaPrade, MD, PhD¹; Patrick M. Morgan, MD¹; Fred A. Wentorf, MS¹; Steinar Johansen, MD²; Lars Engebretsen, MD, PhD²

¹ Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue, R200, Minneapolis, MN 55454. E-mail address for R.F. LaPrade: lapra001@umn.edu
² Department of Orthopaedic Surgery, University of Oslo, Ullevaal University Hospital, 0407, Oslo, Norway

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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants of less than $10,000 from the Sports Medicine Research Fund of the Minnesota Medical Foundation, University of Minnesota, and the Vice President for Research, University of Minnesota. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

Investigation performed at the University of Minnesota, Minneapolis, Minnesota

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2007 Apr 01;89(4):758-764. doi: 10.2106/JBJS.F.00120

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Abstract

Background: The orthopaedic literature contains relatively little quantitative information regarding the anatomy of the posterior aspect of the knee. The purpose of the present study was to provide a detailed description of, and to propose a standard nomenclature for, the anatomy of the posterior aspect of the knee.

Methods: Detailed dissection of twenty nonpaired, fresh-frozen knees was performed. Posterior knee structures were measured according to length, width, and/or distance to reproducible osseous landmarks.

Results: The semimembranosus tendon had eight attachments distal to the main common tendon. The main components were a lateral expansion to the oblique popliteal ligament; a direct arm, which attached to the tibia; and an anterior arm. The oblique popliteal ligament, the largest posterior knee structure, formed a broad fascial sheath over the posterior aspect of the knee and measured 48.0 mm in length and 9.5 mm wide at its medial origin and 16.4 mm wide at its lateral attachment. It had two lateral attachments, one to the meniscofemoral portion of the posterolateral joint capsule and one to the tibia, along the lateral border of the posterior cruciate ligament facet. The semimembranosus also had a distal tibial expansion, which formed a posterior fascial layer over the popliteus muscle. A thickening of the posterior joint capsule, the proximal popliteus capsular expansion, which in this study averaged 40.5 mm in length, connected the posteromedial knee capsule at its attachment at the intercondylar notch to the medial border of the popliteus musculotendinous junction. The plantaris muscle, popliteofibular ligament, fabellofibular ligament, and semimembranosus bursa were present in all specimens.

Conclusions: The anatomy of the posterior aspect of the knee is quite complex. This study provides information that can lead to further biomechanical, radiographic imaging, and clinical studies of the importance of these posterior knee structures.

Figures in this Article

In our referral sports medicine practices, we have treated a number of injuries involving the posterior structures of the knee that have been associated with pain and functional genu recurvatum instability. In an attempt to better understand these injuries, we foundthat the literature provides little quantitative information on posterior knee anatomy and no magnetic resonance imaging studies of these structures. After several dissections of fresh knee specimens revealed that the oblique popliteal ligament was attached to the lateral capsule rather than to the lateral femoral condyle as has been described in several articles^1-4, and after observing that sectioning of this structure caused an observable increase in genu recurvatum, we conducted a thorough literature review of this topic.

The anatomy of the posterior aspect of the knee is a complicated network of dynamic and static stabilizers. Central to its function and structure are the multiple attachments of the semimembranosus and popliteus muscles. Our literature review was complicated not only by competing vocabularies but also by descriptions that detailed a wide range of findings in both the number of structures and the location of their attachments^1,2,5-14. Little attention was paid to the size of these structures, their relationships to surrounding anatomy, and their attachment sites.

It is critical to have an accurate description of these posterior knee structures not only to facilitate the analysis of their functional role through biomechanical studies but also to identify normal and injured structures on magnetic resonance imaging scans in order to determine the etiology of functional problems in patients. Therefore, the present study was conducted to clarify these questions by providing a qualitative and quantitative analysis and to propose a standard nomenclature for the individual anatomic structures of the posterior aspect of the knee.

Materials and Methods

Materials and Methods | Results | Discussion | Acknowledgements | References

Twenty nonpaired, fresh-frozen cadaveric knees with no evidence of previous injury, surgery, or cachexia were utilized for the present study. The average age of the donors at the time of death had been 59.2 years (range, forty-three to seventy-six years). The dissections consisted of identification of the posterior structures of the knee that were located between the posterior borders of the posterior oblique ligament and the tibial course of the superficial medial collateral ligament medially and the medial border of the long head of the biceps femoris and fibula laterally. All structures anterior (deep) to the medial and lateral heads of the gastrocnemius were preserved and identified, except that the neurovascular bundle and the common peroneal nerve were removed. We chose to remove the neurovascular structures because we could not accurately identify and measure the relationships among the posterior knee structures with them still present.

The oblique popliteal ligament and the structures confluent with it were dissected first. The distal attachments of the semimembranosus were identified, and their dimensions were noted. The location of other individual structures and attachments were identified, and the distance from the major structures (measured to the nearest 0.5 mm) to selected osseous landmarks (the midportion and/or lateral border of the posterior cruciate ligament facet, the posterior articular surfaces of the tibial plateaus, and the attachment of the posterior capsule on the femur) was measured with a dial caliper with measurement accuracy to 0.01 mm (L.S. Starrett, Athol, Massachusetts).

Once the superficial posterior structures were measured, the deeper semimembranosus bursa was identified and the distance between the tibial attachment of the direct arm of the semimembranosus and the proximal edge of the medial tibial plateau at the joint line was measured. The presence of a plantaris muscle, fabellofibular ligament, popliteofibular ligament, and a palpable fabella was also recorded. Deeper dissection (to include the functional bundles of the posterior cruciate ligament and the posterior meniscofemoral ligaments) was not performed.

Results

Materials and Methods | Results | Discussion | Acknowledgements | References

Individual posterior knee structures are described below and are grouped into complexes where appropriate. The measurements that are presented are the averages for all structures (Tables I, II, and III).

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TABLE I Quantitative Relationships of the Osseous and Soft-Tissue Posterior and Distal Attachments of the Semimembranosus Muscle at the Knee

Relationship	Measurement*(mm)
Main semimembranosus tendon
Width at bifurcation	11.9 (9.0 to 15.0)
Width of lateral tendinous expansion contributing to oblique popliteal ligament	7.6 (6.0 to 10.0)
Direct arm
Distance distal to posterior joint line	11.6 (5.0 to 16.0)
Width at tibial attachment	21.6 (17.0 to 26.0)
Proximal posterior capsular arm
Distance between edge of proximal attachment to attachment of posterolateral meniscofemoral capsule on lateral femoral condyle	6.8 (1.0 to 15.0)
Distance from inferior border along perpendicular line to the lateral edge of the posterior cruciate ligament facet	15.2 (12.0 to 21.0)
Distal tibial expansion
Length of medial division	107.5 (86.0 to 134.0)
Length of lateral division	107.3 (89.0 to 132.0)