This study documents the gross and histologic structure of the infrapatellar plica, and fat pad, and adds to an earlier report to the COA. The important new findings are that the femoral attachment...

Anterior knee pain (AKP), a multifactorial symptom complex, can be successfully treated surgically. A specific diagnosis often cannot be made, but the pain is linked to an unrecognized common factor in most patients: the mechanical behavior of the non-isometric contents of the anterior compartment of the knee-the fat pad (FP) and infrapatellar plica (IPP). The objective of this presentation is to describe an effective arthroscopic technique that treats AKP by addressing this common factor. The operation consists of release or resection of the IPP, or ligamentum mucosum, which tethers the FP. These highly innervated tissues act together as a hydraulic shock absorber, filling the anterior compartment. They stretch and deform at the extremes of knee motion because of constraint centrally by the non-isometric IPP. These dynamic changes in shape are eliminated when the plica is released or resected. Pain perception is from perturbed nociceptive nerves: pain relief results from de-tensioning these contained nerves by untethering the fat pad. Ascribing pain causation is problematic because morphologic change, such as inflammation, fibrosis, or contracture of these structures, is only present in a minority of cases. Nonetheless, AKP is both physically linked to these central, pain-sensitive structures and relieved by this operation.

Introduction The ligamentum mucosum (LM), or infrapatellar plica, is a non‐isometric structure of the knee joint that traverses from the intercondylar notch of the femur to the infrapatellar fat pad. The LM is composed of dense regular connective tissue, of which four different morphologies have been identified: separate, vertical septum, split, and fenestrated. Microscopically, pathological LM appears fibrotic and calcified, which can lead to impingement, and ultimately may be implicated in the pathogenesis of anterior knee pain. The specific aims of this study are to investigate the anatomical relationship of the LM to neighboring structures, determine whether the histological characteristics of the LM further define its function and its potential role in proprioception, and lastly to perform an in vitro biomechanical analysis of the LM under normal physiological loading. Methodology Fresh‐frozen cadaveric knee specimens (n=14) were dissected to reveal the structures of the joint capsule and to identify the morphology of the ligamentum mucosum. With the knee at 90° flexion, four measurements were recorded in order to examine the important relationships within the joint capsule. The intraclass correlation coefficient was calculated to determine the consistency and reproducibility of the measurements recorded. Maintaining the proximal and distal attachments, two specimens were harvested for histological analysis using standard hematoxylin and eosin, Masson's trichrome for collagen, and mono‐clonal mouse anti‐human neurofilament protein to identify neurons and peripheral nerve endings. Results Overall, 64% of the knees had a LM present. With respect to morphology, 50% of the 14 specimens had a separate type, 14% had a vertical septum type, and the remaining specimens had no LM present, which is consistent with known classification systems. The histological analysis confirmed the LM to be ligamentous, thus being composed of dense regular connective tissue. Preliminary immunohistochemistry results are inconclusive at this time for evidence of peripheral nerves and nerve endings, and the biomechanical properties of LM have yet to be determined. Discussion The role of LM in anterior knee pain is not well documented; however, studies have shown that excising the LM can relieve idiopathic anterior knee pain. With a decrease in elasticity, pathological LM may result in patellar maltracking and instability, ultimately triggering anterior knee pain. Future biomechanical testing will utilize an Instron materials testing machine to load the ligaments under tension at a constant velocity in order to determine the force at which the specimen fails. Thus, the findings from this study can be implemented in models of anterior knee pain, more specifically models of patellar instability and maltracking, to determine the proprioceptive and pathogenic mechanisms of the ligamentum mucosum.

We have described the infrapatellar plica (IPP) of the knee as a non-isometric ligament, attaching the fat pad (FP) to the femur. We had noted during knee arthroscopy that the IPP showed mechanical behavior, stretching and relaxing with motion, and holding the FP against the distal femur. We sought to visualize the kinematics of this behavior using fluoroscopy in cadavers and, in an Institutional Review Board approved study of human volunteers undergoing arthroscopy. With radiographic contrast injected in the IPP, we demonstrated in cadavers and in vivo, that the FP, highly innervated central body (CB), and IPP rotate around the femoral attachment (FA) of the IPP. The fluoroscopic films show a sequence starting in flexion, of stretch and distortion of the IPP and CB, then relaxation throughout mid arc and, remarkable stretch and distortion approaching full extension. This confirmed the non-isometric nature of the IPP. The overlying FP as seen in the second figure was tethered centrally by the IPP, and distorted throughout. Release of the IPP at the FA, which has been shown to reduce or eliminate anterior knee pain (AKP), eliminated the distortion of the FP. This kinematic, demonstrating mechanical perturbation of innervated central structures in the knee, introduces a new central vector, altering traditional patellofemoral biomechanics and suggests an altered concept in the causation of knee pain.

The infrapatellar plica (IPP) is considered to be an embryological remnant, a synovial fold of no mechanical importance. Its tissue characterization has not been described in the English literature. We had noted during knee arthroscopy that the IPP appeared ligament-like, and showed mechanical behavior, stretching and relaxing with motion, and holding the FP against the distal femur. Seeking to determine its gross and microscopic structure and link it to the observed behavior, we dissected 12 cadaver knees, noting for each the gross anatomy, histology of the IPP and attached fat pad (FP). According to the classification by Kim, the IPP types were: 8 separate, 1 split, 2 fenestrated, and 1 vertical septum. The IPP is a non-isometric ligament, with typical ligamentous structure at its femoral attachment (FA), a typical enthesis, and its rope-like central zone (CZ), primarily dense fibrous bundles of collagenous tissue. The structure of the attachment of the IPP to the FP at the central body (CB) is unique and consists of a splaying out of finger-like collagenous septa that merge with those of the FP. There is abundant elastase staining consistent with the distortion associated with knee motion. Lodged in the axillae of these septa are fat lobules similar to those of the FP, but containing a rich plexus of neurovascular bundles, which show wavy redundancy also correlating with the observed mechanical behavior. The IPP/CB/FP complex can be linked to chronic anterior knee pain in that arthroscopic release of the FA relieves the pain in most.

Purpose Anterior knee pain has been relieved by resection of the infrapatellar plica (IPP). The question is: How? The hypothesis is: the IPP acts as an intra-articular ligament, a mechanical link between the forces of knee motion, the fat pad (FP) and the distal femur, holding the FP captive through the arc of motion. Release of the IPP severs this link, allowing the highly innervated FP to move freely. This may allow any underlying pathologic process to heal. Method Anatomic dissection: In 12 knees, the extensor apparatus was released from the femur and retracted distally allowing relationships to be examined. Cadaver studies: Lateral fluoroscopy was used as well as direct arthroscopic visualization to control implantation of tantalum beads or radiographic contrast material in the FP and IPP. The knee was taken through the arc of motion repeatedly. The femoral attachment of the IPP was then released and knee motion repeated. Traction on the extensor apparatus simulated active motion. In-Vivo Study: The IRB approved study of 12 volunteers undergoing planned knee arthroscopy under local anesthesia. Contrast was placed in the FP and IPP under lateral fluoroscopic control. Passive, then active motion then a quads-set manoeuvre was performed. The IPP was resected and knee motion again recorded. Results Knees without IPP (4) demonstrated FPs that were lobular, with lateral bodies, and a central process. The fibrous synovial layer of the capsule bypassed the FP inserting on the superior aspect of the menisci. Knees with an IPP (8) showed a FP that was covered by fibrous synovium. The fibrous elements of the capsule coalesced on either side of the patellar in folds that merged with the alar folds. These fibrous elements ramified over and through the FP and were continuous with the upper portion of the IPP medially and laterally. Inferiorly the lower portion of the IPP merged with fibrous synovium that attached to the superior aspect of the menisci and the inter-meniscal ligament. The cadaver studies demonstrated that the IPP elongated with FP distortion as the knee approached full extension and flexion, and that the IPP was lax through mid arc. Release of the IPP at the femur eliminated almost all of the distortion through the full arc. The In-Vivo study replicated the cadaver observations for passive and active motion. The quads set manoeuvre caused further distortion of the FP with the patella moving one cm proximally. Release of the IPP eliminated FP distortion. Conclusion The IPP seems to act as a true ligamentum mucosum. By virtue of its central femoral attachment if captures the FP against the end of the femur, loosely in mid arc, but with distortion of the FP and stretch of the IPP approaching full flexion and extension. This has been demonstrated in both cadavers and in in-vivo for the first time. Any pathologic process affecting the highly innervated FP will likely be improved by removal of the capture effect of the IPP.

Have you previously submitted this study for another congress?: Yes Which Congress?: Canadian Orthopaedic Association Annual Meeting, July 2011; 15th ESSKA Congress Presentation Method Preference: Oral or E-Poster INTRODUCTION: Wachtler3 in 1979 described the histology of the IPP and discussed its function. Beyond the histology, he injected the fat pad (FP) and noted from his observations that “...from a mechanical and teleological point of view, the IPP may have little relevance...” By contrast, anterior knee pain has been relieved by resection of the infrapatellar plica (IPP)1,2. The question is: How? The hypothesis is: that the IPP acts as an intra-articular ligament, a mechanical link between the motors of knee motion, the fat pad (FP) and the distal femur, holding the FP captive through the arc of motion. Release of the IPP severs this link, allowing the highly innervated FP to move freely. This study reports on replication of Wachtler's study with the addition of in-vivo verification. The remarkable videos are at variance with Wachtler's opinion and suggest a distinct mechanical role for this structure. OBJECTIVES: In cadaver knees to inject the FP and IPP with radiographic contrast, and observe passive motion through lateral fluorscopy. In awake volunteers undergoing arthroscopy, to repeat the experiment with active motion and a quads set manouevre. METHODS: Cadaver studies: In 2 embalmed cadaver knees arthroscopy was performed to verify normal anatomy and the presence of an IPP. Direct arthroscopic visualization was used to control implantation of contrast material in the FP and IPP. The knee was taken through the arc of motion and recorded through lateral fluoroscopy. The femoral attachment of the IPP was then released and knee motion repeated and recorded. In-Vivo Study: In an IRB approved study of 12 volunteers undergoing planned knee arthroscopy under local anesthesia, contrast was placed in the FP and IPP under lateral fluoroscopic control. Passive, then active motion then a quads-set manoeuvre was performed. The IPP was resected and knee motion again recorded. RESULTS: Videos from the cadaver studies demonstrated that the IPP elongated with FP distortion as the knee approached full extension and flexion, and that the IPP was lax through mid arc. Release of the IPP at the femur eliminated almost all of the distortion through the full arc. Success was achieved in only 4 patients in the In-Vivo Study. However, the videos replicated the cadaver observations for passive and, for the first time in living patients, active motion. The quads set manoeuvre caused further distortion of the FP with the patella moving one cm proximally. Release of the IPP eliminated FP distortion. CONCLUSION: Knee motion was recording by lateral fluoroscopy in 2 cadaver, and 4 in-vivo knees. The videos showed in all instances stretch and deformation of the FP and IPP as the knees approached full extension and flexion. This unexpected non-isometric mechanical behaviour of the IPP shows that by virtue of is central attachment it holds the FP captive against the femur. Release of the IPP eliminates the mechanical effect of the IPP on the FP. Pain relief can be through denervation, or through release of the innervated central body of the FP. REFERENCES: 1. Boyd CR, Eakin C, Matheson GO. Infrapatellar plica as a cause of anterior knee pain. Clinical Journal of Sport Medicine. 2005;15:98-103. 2. Demirag B, Ozturk C, Karakayali M. Symptomatic infrapatellar plica. Knee Surgery, Sports Traumatology, Arthroscopy. 2006;14:156-160. 3. Wachtler F. Plica synovialis infrapatellaris in man. Acta Anat (Basel). 1979;104:451-459.

The role of arthroscopy in the preconflict deployment of a large number of military troops is not well defined. Between September 1990 and January 1991, while deployed to the Persian Gulf for Operation Desert Shield 73 patients underwent on-board elective arthroscopy on the USNS Mercy. There were 71 men and two women with an average age of 27 years (range 19-47). Indications for arthroscopy included clinical diagnosis of meniscus tear, acute hemarthrosis, chronic effusion, and intra-articular loose body. Findings at the time of arthroscopy included 34 patients (47%) with meniscus tears; 17 (23%) with anterior cruciate ligament tears; five (7%) with isolated grade II-IV chondromalacia involving the patella, trochlea, femoral condyles, or tibial plateaus; six (8%) with synovitis; four (5%) with osteochondritis dissecans of the medial femoral condyle; two (3%) with a medial retinacular tear secondary to patella dislocation; and 10 (14%) with normal arthroscopic examinations. Forty-nine patients (66%) were returned to duty at an average of 6 days postoperatively, obviating the need to evacuate these patients from the Middle East theatre.

A 26-year-old man who was a military parachutist, experienced a parachuting accident with collapse of his parachute at a height of 600 ft. The particular biomechanics of his impact were favourable. He sustained an L3 wedge compression fracture and pubic symphyseal diastasis. He recovered fully over 10 months and was able to return to full duties, including parachuting. The biomechanics of human impact during vertical deceleration and the associated injuries are discussed in detail with reference to this case and parachutists in general. The relevance of standard parachuting drills and the importance of properly executed malfuction drills are addressed.

Between September 1990 and January 1991, while deployed to the Persian Gulf for Operation Desert Shield, 118 patients underwent arthroscopic surgery of the knee on the U.S. Naval Hospital Ships USNS Mercy and USNS Comfort. There were 113 men and 5 women, with an average age of 28 years (range, 19-59 years). The most common findings at the time of arthroscopy were meniscus tears (53%), anterior cruciate ligament tears (29%), and normal arthroscopic examinations (9%). There were three complications, two hemarthroses and one superficial portal site infection. Seventy patients (59%) were able to be returned to duty at an average of 6 days post-operatively, obviating the need to evacuate these patients out of the Middle East theater to Europe or the United States, thus avoiding additional delay, expense, and loss of the service member to his military unit.

Holmes, C. A.; Bosse, M. J.; McLaughlin, C. S.; Buckley, S. L.; Jones, A. A.; Culp, R. W.; Smallman, T. Author Information

This paper reports on three cases of symptomatic low back pain in three paratroopers in association with bilateral L5 spondylolysis and L5 on S1 spondylolisthesis. The controversy regarding the etiology of this lesion as well as the problems of establishing causality when associated with parachuting injuries are discussed. These cases raise the issue of whether routine lumbar spine roentgenography should be performed as part of the pre-course medical screening prior to an individual undertaking basic parachutist training, and stress the need for further study of the relevance of these lesions in military parachuting.

Stress fracture of the pars interarticularis is an increasing cause of disability in highly competitive adolescent athletes. We have documented this lesion in 14 adolescent athletes engaged in repetitive training and competition exercises involving flexion/extension of the lumbar spine. An in vivo spinal muscle torque study in 11 normal adolescent girls also revealed mean torque values of 22.6 Nm for left lateral flexion and 27.4 Nm for hyperextension. The most common sports resulting in this lesion were gymnastics and hockey. In four patients the lesion was bilateral, and in 10 it was unilateral. Five of the unilateral lesions went on to heal with immobilization in a thoracolumbar spinal orthoses; however, none of the four bilateral lesions or the remaining five unilateral lesions healed in spite of 3 months of immobilization.