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Communication Between the Proximal Tibiofibular Joint and Knee via the Subpopliteal Recess: MR Arthrography with Histologic Correlation and Stratigraphic Dissection

¹ Department of Radiology, University of California, San Diego, VA San Diego Healthcare System, San Diego, CA 92161.
² Present address: Department of Radiology, Atatürk State Teaching Hospital, 69 sok. No: 33 A Blok, Daire: 17 Uckuyular/Izmir, Turkey 35350.
³ Department of Applied Anatomy, Center of Anatomy and Cell Biology, Medical University of Vienna, Vienna, Austria.

Received November 8, 2007; accepted after revision February 23, 2008.

 
Address correspondence to B. Dirim (bernadirim{at}gmail.com).

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Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
OBJECTIVE. The anatomy and functional importance of the proximal tibiofibular joint (TFJ) have rarely been emphasized. Specifically, the detailed anatomic basis and MRI findings of the communication between the proximal TFJ and the knee have not been defined in the literature. To investigate such communication, anatomic and histologic correlation with MRI findings in frozen specimens and dissections of embalmed specimens was used in the study.

MATERIALS AND METHODS. Twelve frozen knees were studied on MR arthrography. MR images of each specimen were compared with anatomic slices and histologic sample analysis. Dissection of an additional 28 embalmed specimens was performed to further investigate communication and the anatomy of the proximal TFJ.

RESULTS. Communication between the proximal TFJ and the knee was observed in 27.5% of all anatomic specimens. It occurred via the subpopliteal recess and was related to a defect in the posterior ligament of the fibular head in all specimens. Evidence of an injury was apparent on MR images and was proven on histologic examination in 9% of the anatomic specimens that had such communication.

CONCLUSION. The frequency of the communication between the proximal TFJ and knee via the subpopliteal recess related to a defect in the posterior ligament of the fibular head was found to be 27.5%. Evidence of an injury was present in 9% of anatomic specimens that had such communication. Injury to the posterior ligament of the fibular head and instability of the proximal TFJ may accompany a variety of knee injuries. Knowledge of the detailed anatomic appearance and MRI characteristics of the structures related to the proximal TFJ is key to identifying injuries to these structures.

Keywords: emergency medicine • knee • MR arthrography • sports medicine • subpopliteal recess • tibiofibular joint • trauma

Introduction

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MRI of the knee is commonly undertaken for the analysis of ligaments, menisci, articular cartilage, and bones, especially in cases of trauma. Although the proximal tibiofibular joint (TFJ) is often in the field of view during such MRI studies, this articulation often seems to be overlooked during routine analysis. Indeed, only a few published reports related to the proximal TFJ exist in the radiologic literature [1–3].

Communication between the proximal TFJ and the knee joint may be identified in some fetuses and exists in approximately 10% of adults [3, 4]. Gruber [5], in 1845, described such communication in 11 of 80 (14%) dissected knees. In other investigations, the frequency of such communication has been reported to be between 12% and 64% [6–8]. Unfortunately, the detailed anatomic basis and MRI findings related to such communication have not, to our knowledge, been described.

Our study was designed on the basis of the clinical observation that in multiple posterolateral corner injuries fluid was seen extending from the knee joint cavity to the proximal TFJ cavity. This study was performed to analyze the frequency, pattern, and cause of the communication between the proximal TFJ and the knee joint and to describe the anatomic and histologic details of the adjacent structures in anatomic specimens using MRI and MR arthrography.

Materials and Methods

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Fresh Frozen Anatomic Specimens
Twelve fresh frozen anatomic specimens of human knees from 10 adults (six women and four men; eight left knees and four right knees; age at the time of death, range, 64–90 years and mean, 80.3 years) were obtained. Frontal and lateral radiographs were obtained of each specimen and evaluated in consensus by two authors (with 30 and 10 years of experience, respectively, in interpreting musculoskeletal radiographs) to ensure that the knee joint was not affected by surgical alterations or pathologic abnormalities. The cadaveric specimens were immediately frozen at –40°C (Bio-Freezer, Forma Scientific). They were allowed to thaw for 24 hours at room temperature before MRI. Subsequently, the anatomic specimens were prepared according to methods described in the literature [9]. The knee specimens were obtained and used according to institutional guidelines, and informed consent for research was obtained from relatives of the deceased.

MR images were acquired with a 1.5-T superconducting magnet (Signa or Signa LX Horizon, software version 8.3, GE Healthcare) using a 6.5-inch (16.5-cm) standard knee coil (Dia Coil, Medical Advances). All fresh-frozen anatomic knee specimens were imaged in a neutral supine position. Imaging was performed in the coronal, transverse, and sagittal planes. The MRI protocol consisted of T1-weighted spin-echo sequences (TR/TE range, 550/20–21). To acquire high-spatial-resolution images, a section thickness of 1.5 mm, intersection gap of 0.5 mm, field of view of 12 x 12 cm, and data acquisition matrix of 512 x 256 pixels were used.

T1-weighted spin-echo MR images with and without fat suppression in all three planes were acquired before and after intraarticular administration of a dilute gadolinium-containing contrast agent (gadopentetate dimeglumine [Magnevist, Schering]). To distend the joint and its recesses fully, approximately 55–60 mL of a mixture of gadopentetate dimeglumine and saline (1:200 dilution) was injected into the joint while using manual pressure and an 18-gauge needle. MRI began within 5 minutes after the injection.

After completion of the MR scans, the cadaveric knee specimens were frozen again at –40°C (Bio-Freezer) for more than 120 hours. The frozen knee specimens were then sectioned using a band saw (model B12, Butcher) into 2-mm-thick slices in the sagittal (n = 7), axial (n = 3), and coronal (n = 2) planes corresponding closely to the MR images. After debris was rinsed from the surface of the specimens, the sections were thawed and then each slice was imaged with high-spatial-resolution radiography (Faxitron, Hewlett-Packard) and photographed under floodlighting with a digital camera (Coolpix 990, Nikon). To determine the presence and precise site of any communication between the proximal TFJ and the knee joint, the findings on MR images and radiographs of each specimen were compared with the findings derived from visual inspection of the anatomic slices by two authors.

To analyze the pattern of communication between the proximal TFJ and the knee and its relation to adjacent structures, histologic samples of this area were collected in four knee specimens. Samples were collected from three knees in which a communication existed between these two joints and one knee in which such a communication was absent. The samples were suspended in a 10% formalin solution, embedded in paraffin, and sectioned further into 5-µm-thick slices. Histologic slices were stained with H and E and analyzed at light microscopy (magnification, x2–x10), in consensus, by a musculoskeletal radiologist and an orthopedic pathologist, each with 30 years of experience. The examiners recorded the presence or absence of a communication between the proximal TFJ and the knee and the histologic nature of the region of communication.

Stratigraphic Dissection of Embalmed Specimens
In addition, 28 anatomic knee specimens fixed with a mixture of formol and carbol underwent stratigraphic dissection. To avoid sampling and observer bias, the knees were randomly selected from available cadavers by anatomy assistants not involved in the research group. Only separated single knees were then transferred and dissected by the authors. In sum, 11 right and 17 left embalmed knee specimens taken from donors of both sexes with an average age of 75 years at the time of death were investigated. Informed consent was individually given by will of each of the body donors.

During stratigraphic dissection each specimen was photographed step by step. The anterior and posterior portions of the fibrous capsule of the proximal TFJ were identified by carefully removing all the superficial structures covering the joint. On the posterior aspect, all muscles except the popliteus muscle were detached from their sites of origin. Subsequently 2 mL of concentrated Romanowsky-Giemsa stain (a mixture of eosin, methylene blue, methylene azure, and methylene violet originally designed as a nuclear stain) was injected into the joint space by puncture of the anterior ligament of the fibular head—that is, by piercing the anterior part of the fibrous and synovial capsule. To properly localize the narrow joint space, the anterior edge of the fibular collateral ligament was found as a useful guiding structure. Immediately after the injection, the popliteus muscle was carefully detached from its tibial origin and the subpopliteal recess and popliteal hiatus were inspected. A communication between the proximal TFJ and the knee joint via the subpopliteal recess was diagnosed by leakage of the blue stain into the recess.

Results

Top Abstract Introduction Materials and Methods Results Discussion References

 
Fresh Frozen Anatomic Specimens
With MRI, communication between the proximal TFJ and the knee joint was verified by the presence of contrast material in the proximal TFJ after its injection into the knee joint. The communication between the two articulations was shown in three (25%) (two women and one man; mean age at the time of death [± SD], 85.5 ± 5.8 years) of the 12 fresh frozen specimens (Figs. 1A, 1B, 1C, 1D, and 1E).

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —Left knee from cadaver of 79-year-old man. From lateral (A) to medial (D) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show contrast material in proximal tibiofibular joint (TFJ) cavity (open arrow, B–D), which indicates communication between proximal TFJ and knee joint. Defect in medial part of posterior ligament of fibular head (solid white arrows) and subpopliteal recess (black arrow, D) are also seen. T = tibia, F = fibula.

View larger version (140K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —Left knee from cadaver of 79-year-old man. From lateral (A) to medial (D) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show contrast material in proximal tibiofibular joint (TFJ) cavity (open arrow, B–D), which indicates communication between proximal TFJ and knee joint. Defect in medial part of posterior ligament of fibular head (solid white arrows) and subpopliteal recess (black arrow, D) are also seen. T = tibia, F = fibula.

View larger version (150K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —Left knee from cadaver of 79-year-old man. From lateral (A) to medial (D) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show contrast material in proximal tibiofibular joint (TFJ) cavity (open arrow, B–D), which indicates communication between proximal TFJ and knee joint. Defect in medial part of posterior ligament of fibular head (solid white arrows) and subpopliteal recess (black arrow, D) are also seen. T = tibia, F = fibula.

View larger version (151K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D —Left knee from cadaver of 79-year-old man. From lateral (A) to medial (D) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show contrast material in proximal tibiofibular joint (TFJ) cavity (open arrow, B–D), which indicates communication between proximal TFJ and knee joint. Defect in medial part of posterior ligament of fibular head (solid white arrows) and subpopliteal recess (black arrow, D) are also seen. T = tibia, F = fibula.

View larger version (213K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1E —Left knee from cadaver of 79-year-old man. Anatomic photograph of cadaveric knee specimen shows defect within posterior ligament of fibular head (black arrows) that led to communication between proximal TFJ (white arrow) and knee joint via subpopliteal recess (arrowheads). P = popliteal tendon, F = fibula, T = tibia.

View larger version (123K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —Knee from cadaver of 74-year-old woman. From lateral (A) to medial (C) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show intact posterior ligament of fibular head (arrow), subpopliteal recess (arrowhead), tibia (T), and fibula (F).

View larger version (127K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —Knee from cadaver of 74-year-old woman. From lateral (A) to medial (C) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show intact posterior ligament of fibular head (arrow), subpopliteal recess (arrowhead), tibia (T), and fibula (F).

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —Knee from cadaver of 74-year-old woman. From lateral (A) to medial (C) views, serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show intact posterior ligament of fibular head (arrow), subpopliteal recess (arrowhead), tibia (T), and fibula (F).

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D —Knee from cadaver of 74-year-old woman. Anatomic photograph of cadaveric knee specimen shows intact posterior ligament of fibular head (arrow), subpopliteal recess (arrowheads), popliteal tendon (P), tibia (T), and fibula (F).

View larger version (104K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2E —Knee from cadaver of 74-year-old woman. Photomicrograph of histologic section shows intact posterior ligament of fibular head (straight arrow), subpopliteal recess (arrowheads), popliteofibular ligament (curved arrow), popliteal tendon (P), cavity of knee joint (KJ), cavity of proximal tibiofibular joint (PTFJ), tibia (T), and fibula (F). (H and E, original magnification)

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —Right knee from cadaver of 79-year-old man. Sagittal T1-weighted spin-echo MR image (TR/TE, 550/20) with fat suppression obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen shows popliteal hiatus (arrowheads), subpopliteal recess (arrows), popliteal tendon (P), femur (FM), lateral meniscus (LM), tibia (T), and fibula (F).

View larger version (151K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —Right knee from cadaver of 79-year-old man. Anatomic photograph of cadaveric knee specimen shows subpopliteal recess (arrows), anteroinferior popliteomeniscal fascicle (arrowheads), lateral meniscus (LM), popliteal tendon (P), femur (FM), tibia (T), and fibula (F).

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C —Right knee from cadaver of 79-year-old man. Coronal T1-weighted spin-echo MR image (550/20) with fat suppression obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen shows popliteal hiatus (black arrowheads), subpopliteal recess (straight arrow), anteroinferior (curved arrow) and posterosuperior (white arrowhead) popliteomeniscal fascicles, popliteal tendon (P), lateral meniscus (LM), femur (FM), tibia (T), and fibula (F).

On histologic analysis, the posterior ligament of the fibular head was observed as a ligamentous structure that was located between the posterior surface of the fibular head and the posterior aspect of the lateral condyle of the tibia. It was intact in one knee that revealed no communication between the proximal TFJ and knee on MR images and anatomic inspection. The posterior ligament of the fibular head separated the subpopliteal recess from the proximal TFJ (Figs. 2A, 2B, 2C, 2D, and 2E). A defect within the posterior ligament of the fibular head was seen in all three knees in which a communication between the proximal TFJ and the knee joint had been documented.

The popliteal hiatus and fascicles of the lateral meniscus were visualized around the subpopliteal recess in all cadaveric specimens. The popliteal hiatus is an aperture that was defined by the fascicles of the lateral meniscus, allowing the popliteal tendon to course from the tibia below to its femoral attachment above. The popliteal hiatus appeared as a contrast-containing structure between the popliteus tendon and the body and posterior horn of the lateral meniscus in the MR arthrographic images in all the cadaveric specimens (Figs. 3A, 3B, and 3C). The anteroinferior and posterosuperior popliteomeniscal fascicles were identified on MR arthrography in all 12 specimens (100%) in both the sagittal and coronal planes (Figs. 3A, 3B, and 3C). The posterosuperior popliteomeniscal fascicle extended from the posterosuperior corner of the posterior horn of the lateral meniscus to the posterior capsule of the knee joint above the popliteus tendon, and it formed the roof of the popliteal hiatus. The anteroinferior popliteomeniscal fascicle extended inferoposteriorly from the body of the lateral meniscus to the popliteus tendon, and it formed the floor of the popliteal hiatus. The subpopliteal recess was seen just below the anteroinferior popliteomeniscal fascicle and the popliteal hiatus was seen just above the anteroinferior popliteomeniscal fascicle in all MR arthrographic images and anatomic slices (Figs. 3A, 3B, and 3C). The anteroinferior popliteomeniscal fascicle was intact in 11 of 12 (92%) specimens. Disruption of the anteroinferior popliteomeniscal fascicle was observed in MR arthrographic images and anatomic slices in one of the 12 (8%) fresh frozen anatomic specimens (Figs. 4A, 4B, 4C, 4D, and 4E).

View larger version (171K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —Knee from cadaver of 90-year-old woman. Anatomic photograph of cadaveric knee specimen shows ruptured anteroinferior popliteomeniscal fascicle (arrows), lateral meniscus (LM), popliteal tendon (P), femur (FM), tibia (T), and fibula (F).

View larger version (159K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —Knee from cadaver of 90-year-old woman. Lateral (B) and medial (C) serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show ruptured anteroinferior popliteomeniscal fascicle (arrow, B), detachment of popliteofibular ligament from fibular head (arrowhead, B), ruptured posterior ligament of fibular head (arrowheads, C) which led to communication (arrow, C) between knee joint and proximal tibiofibular joint, lateral meniscus (LM, B), popliteal tendon (P, B), femur (FM, B), tibia (T), and fibula (F).

View larger version (145K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C —Knee from cadaver of 90-year-old woman. Lateral (B) and medial (C) serial sagittal T1-weighted spin-echo MR images (TR/TE, 550/20) obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen show ruptured anteroinferior popliteomeniscal fascicle (arrow, B), detachment of popliteofibular ligament from fibular head (arrowhead, B), ruptured posterior ligament of fibular head (arrowheads, C) which led to communication (arrow, C) between knee joint and proximal tibiofibular joint, lateral meniscus (LM, B), popliteal tendon (P, B), femur (FM, B), tibia (T), and fibula (F).

View larger version (113K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4D —Knee from cadaver of 90-year-old woman. Sagittal T1-weighted spin-echo MR image (550/20) with fat suppression obtained after injection of gadolinium-containing contrast material in cadaveric knee specimen shows ruptured posteroinferior popliteomeniscal fascicle (solid arrow), ruptured posterior ligament of fibular head (arrowheads) that led to communication (open arrow) between knee joint and proximal tibiofibular joint, lateral meniscus (LM), femur (FM), tibia (T), and fibula (F).

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4E —Knee from cadaver of 90-year-old woman. Photomicrograph of histologic section shows curved appearance of margin of ruptured posterior ligament of fibular head (arrowheads), which indicates posttraumatic fibrosis, and degenerative cystic changes in ruptured ligament (arrows). (H and E, x10)

Table 1 summarizes the descriptive statistics of the fresh frozen specimens.

Stratigraphic Dissection of Embalmed Specimens
In the majority of embalmed specimens (71.4%), no communication between the knee and the proximal TFJ was found to exist. In these 20 negative cases (eight right and 12 left knees), the posterior wall of the proximal TFJ, which is formed by the posterior ligament of the fibular head, completely separated the proximal TFJ from the subpopliteal recess (Fig. 5A).

View larger version (130K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —Dissection photos of embalmed knee specimens. Photograph of embalmed knee specimen, posterior aspect, of 77-year-old man. Subpopliteal recess has been opened by carefully mobilizing popliteus muscle. Note strong posterior ligament of fibular head (probe) lined with synovial membrane separating subpopliteal recess (SR) from proximal tibiofibular joint (TFJ). F = fibular head, P = popliteus muscle, asterisk = popliteal hiatus.

View larger version (146K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —Dissection photos of embalmed knee specimens. Photograph of embalmed knee specimen of 78-year-old man shows total dehiscence of posterior ligament of fibular head. Probe shows open communication between proximal TFJ and subpopliteal recess. P = popliteus muscle, asterisk = popliteal hiatus.

View larger version (141K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C —Dissection photos of embalmed knee specimens. Photograph of embalmed knee specimen, posterior view, of 80-year-old woman. Note stain emerging from proximal TFJ via very thin and translucent membrane incompletely separating subpopliteal recess from proximal TFJ. Posterior ligament of fibular head is absent. F = fibular head, P = popliteus muscle.

Table 2 summarizes the descriptive statistics of the embalmed specimens.

Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Only a few published reports related to the proximal TFJ exist in the radiologic literature [1–3], and the anatomy and functional importance of the proximal TFJ are not clear. Specifically, the potential communication between the proximal TFJ and the knee joint has rarely been emphasized in the literature [3, 5–8]. To our knowledge, the detailed anatomic basis, histologic basis, and MRI findings of such communication have not been fully described in previous works.

The proximal TFJ is a plane joint approximately between the lateral condyle of the tibia and the head of the fibula. The fibrous capsule is attached to the margins of the articular facets on the tibia and fibula; the capsule is thicker anteriorly than posteriorly. The capsule is strengthened by anterior and posterior ligaments of the fibular head. The anterior ligament consists of two or three flat bands that pass obliquely upward from the anterior surface of the head of the fibula to the anterior surface of the lateral condyle of the tibia. The posterior ligament is a thick band that passes obliquely upward from the posterior surface of the head of the fibula to the posterior surface of the lateral condyle of the tibia. It is covered by the popliteus tendon. These ligaments are not entirely separable from the fibrous capsule. In traditional anatomic descriptions, the communication between the proximal TFJ and the knee joint via the subpopliteal recess is described as an occasional occurrence related to a developmental deficiency of the posterior ligament of the fibular head [4, 10].

In our study, we detected a communication between the proximal TFJ and the knee joint in 27.5% of all anatomic specimens. This included three of the 12 fresh frozen specimens that were examined by gross sectional anatomic and histologic correlation with MR arthrography images and eight of the 28 embalmed specimens of human legs that were evaluated by dissection. In the early work of Gruber [5], an open communication between the proximal TFJ and knee joint was reported to occur in approximately 14% of persons. The frequency of a communication between these two articulations has been reported to be between 12% and 64.3% in other reports [6–8]. Only one of these investigations used MR arthrography images to prove the existence of such a communication [8].

View larger version (128K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A —Embalmed knee specimen, lateral aspect, of 75-year-old man. Note different position of fibular head during dorsiflexion (A) and plantarflexion (B) of foot indicating functional significance of proximal tibiofibular joint, guaranteeing full range of movement in talocrural joint. In lateral rotation of fibula accompanying dorsiflexion of ankle, posterior ligament of fibular head is relaxed, whereas it becomes gradually taut during medial rotation of fibula which, in turn, occurs in plantarflexion of ankle.

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B —Embalmed knee specimen, lateral aspect, of 75-year-old man. Note different position of fibular head during dorsiflexion (A) and plantarflexion (B) of foot indicating functional significance of proximal tibiofibular joint, guaranteeing full range of movement in talocrural joint. In lateral rotation of fibula accompanying dorsiflexion of ankle, posterior ligament of fibular head is relaxed, whereas it becomes gradually taut during medial rotation of fibula which, in turn, occurs in plantarflexion of ankle.

Different descriptions of the subpopliteal recess exist, however. It is the classic description of Henle [11] that coincides exactly with the real anatomic situation. Contemporary descriptions obviously fail to distinguish the subpopliteal recess from the smaller and more proximally situated popliteal hiatus, which is represented by a small slit between the popliteus tendon and the lateral meniscus [4]. Thus, the popliteal hiatus is only the proximal entrance into the subpopliteal recess.

The posterior ligament of the fibular head was covered by the subpopliteal recess and was best observed on sagittal MR images and MR arthrography images as a low-signal-intensity band between the posterior surface of the lateral condyle of the tibia and the posterior surface of the fibular head. A defect within the posterior ligament of the fibular head was observed in all 11 specimens that had a communication between the subpopliteal recess and the proximal TFJ. Evidence of an injury was apparent in one of the 11 (9%) anatomic specimens that had had such communication (three of 12 fresh frozen anatomic specimens and eight of 28 embalmed specimens). In the 91% of our anatomic specimens with such a communication, the posterior ligament of the fibular head was defective and no evidence of trauma was observed; however, existence of the communication in these specimens without any evidence of trauma suggests that such a communication may also be caused by a developmental deficiency of the posterior ligament of the fibular head.

Functionally the proximal TFJ is related to both the knee and the talocrural joint. In contrast to lower vertebrates (i.e., sauropsida) the function of the fibula related to the knee joint in humans is rather limited [12]. In terms of human knee joint function, the fibular head merely serves as an attachment for the fibular collateral ligament and the adjoining tendon of the biceps femoris muscle as well as of the arcuate popliteal ligament and the lateral meniscus [13]. Moreover, slight conjoint axial rotation of the fibula in the proximal tibiofibular joint is an integral part of the talocrural joint.

As shown in Figures 6A and 6B, the fibula is externally rotated in dorsiflexion of the foot, thus allowing the broader anterior part of the trochlea tali to pass within the mortise formed by the malleoli. Thus, one of the primary functions of the proximal TFJ is believed to be dissipation of torsion force applied at the ankle joint [14]. The injury of the posterior and anterior ligaments of the fibular head may lead to instability of the proximal TFJ and also to deficiency of the active movements of the talocrural joint. According to the investigation of Espregueira-Mendes and da Silva [15], the proximal TFJ is responsible for one sixth of the axial load applied to the knee.

We recognize that limitations of our study include the absence of clinical history and the advanced age (mean age at death for 40 specimens, 77 years) of the adults from whom the specimens were acquired, which might have increased the incidence of degenerative changes. All specimens, however, were screened with radiographic studies. Thirty-three of all knee specimens (82.5%) did not have more than age-dependent alterations in both joints: There was neither extensive loss of cartilage nor an unreasonably high degree of osteophytes. In seven of all knee specimens (17.5%), manifest degenerative changes were inspected in the proximal TFJ and the knee joint. None of these seven knees had a communication between the proximal TFJ and the knee joint.

The results of our study show that the communication between the proximal TFJ and the knee joint in 27.5% of anatomic specimens via the subpopliteal recess was associated with a defect of the posterior ligament of fibular head. These specimens included three of the 12 fresh-frozen specimens that were examined by gross sectional anatomic and histologic correlation with MR arthrography images and eight of the 28 embalmed specimens of human legs that were evaluated by dissection. Moreover, our study describes the anatomic structures related to the proximal TFJ and the subpopliteal recess—that is, the anterior ligament of the fibular head, popliteal hiatus, and popliteomeniscal fascicles—using MR arthrographic images.

Acknowledgments
 
We gratefully acknowledge the help of Debra Trudell and Parvitz Haghighi for their collaboration and the help of Klaus S. Wolff and Arne Langer for their very skillful dissections.

References

Top Abstract Introduction Materials and Methods Results Discussion References

 

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