346 Br J Sports Med 1998;32:346–355 Br J Sports Med: first published as 10.1136/bjsm.32.4.346 on 1 December 1998. Downloaded from OCCASIONAL PIECE Patellar tendinopathy: some aspects of basic science and clinical management School of Human Kinetics, University of K M Khan, N MaVulli, B D Coleman, J L Cook, J E Taunton British Columbia, Vancouver, Canada K M Khan J E Taunton Tendon injuries account for a substantial tendinopathy, and the remainder to tendon or Victorian Institute of proportion of overuse injuries in sports.1–6 tendon structure in general. Sport Tendon Study Despite the morbidity associated with patellar Group, Melbourne, tendinopathy in athletes, management is far Victoria, Australia 7 Anatomy K M Khan from scientifically based. After highlighting The patellar tendon, the extension of the com- J L Cook some aspects of clinically relevant basic sci- mon tendon of insertion of the quadriceps ence, we aim to (a) review studies of patellar femoris muscle, extends from the inferior pole Department of tendon pathology that explain why the condi- of the patella to the tibial tuberosity. It is about Orthopaedic Surgery, tion can become chronic, (b) summarise the University of Aberdeen 3 cm wide in the coronal plane and 4 to 5 mm Medical School, clinical features and describe recent advances deep in the sagittal plane. Macroscopically it Aberdeen, Scotland, in the investigation of this condition, and (c) appears glistening, stringy, and white. United Kingdom outline conservative and surgical treatment NMaVulli options. BLOOD SUPPLY Department of The blood supply has been postulated to con- 89 Medicine, University tribute to patellar tendinopathy. The patellar of Melbourne, Royal Method tendon receives its vascularisation through the Melbourne Hospital, A computerised literature search of the entire anastomotic ring which lies in the thin layers of Parkville, Victoria, MEDLINE database, covering the years 1966 loose connective tissue covering the dense Australia to the present, was conducted for this review. fibrous expansion of the rectus femoris. The B D Coleman Table 1 lists the keywords used in the search. J L Cook main contributors are the medial inferior All relevant articles were retrieved, either genicular, lateral superior genicular, lateral GriYths University, locally or by interlibrary loan. The search was inferior genicular, and the anterior tibial recur- 10 11 Gold Coast, not limited to the English literature, and rent artery. The blood supply to the http://bjsm.bmj.com/ Queensland, Australia articles in all journals were considered. The proximal portion of the patellar tendon enters J L Cook authors’ personal collections of papers and any precisely around the region that is most relevant personal correspondence were also Allan McGavin Sports commonly aVected by patellar tendinopathy— Medicine Centre, included. The references selected were re- the proximal posterior aspect of the tendon. University of British viewed by the authors, and judged on their A commonly held belief is that the patellar Columbia, Vancouver, contribution to the body of knowledge of this tendon has a “relatively avascular osseotendi- Canada topic. The conduct and validity of any clinical nous junction” (Scapinelli11 quoted from J E Taunton studies was carefully considered, and the 9 11 McLoughlin et al ). Scapinelli reported that, on September 28, 2021 by guest. Protected copyright. outcomes of management protocols were care- Correspondence to: although the distal attachment of the patellar Dr K Khan, School of fully scrutinised. Case reports were excluded, tendon to the tibial tuberosity includes an Human Kinetics, University unless they mentioned a specific association “avascular zone between ligament and bone”, of British Columbia, 6081 with the condition which was thought to be University Boulevard, the proximal attachment abuts the inferior half Vancouver V6T 1Z1, relevant to the discussion. Only papers that of the patella and the infrapatellar fat pad, both Canada. made a significant contribution to the under- of which are richly vascularised. Thus the standing of this condition were included in the proximal patellar tendon is well vascularised. Accepted for publication 27 May 1998 review. This left a total of 315 publications, Blood flow at rest, however, does not necessar- 52 of which were directly related to patellar ily correlate with blood flow during activity. Table 1 Keywords used to search the MEDLINE database Recent technical advances could permit fur- ther study of patellar tendon vasculature at rest Keywords and during quadriceps stretch and Patellar tendon Extracellular matrix Tendinitis contraction.12 Athletic injuries Incidence Tendon Biomechanics Postoperative complications Tendon injuries Collagen Patellar tendinopathy Mechanical loading in sport Subheadings Tendon displays a characteristic stress-strain Abnormalities Growth and development Pathophysiology curve113(fig 1). The classic crimped configura- Anatomy and histology Injuries Surgery tion of collagen fibres and fibrils at rest disap- Blood supply Innervation Transplantation 414 Chemistry Metabolism Ultrasonography pears when tendon is stretched by about 2%. Cytology Pathology Ultrastructure With further stretch to about 5% elongation— Drug eVects Physiology Imaging that is, load in sport—tendon fibres become Magnetic resonance imaging more parallel and the tendon has a relatively Patellar tendinopathy 347 Br J Sports Med: first published as 10.1136/bjsm.32.4.346 on 1 December 1998. Downloaded from Tendon rupture ferences in nomenclature rather than a paucity of data. Macroscopically, the patellar tendon of Overuse injury patients with jumper’s knee contain soft,23 >8% yellow-brown, and disorganised tissue23–25 evi- 5–8% dent even to the naked eye.26–31 This macro- Physiological scopic appearance is commonly labelled “mu- 3–5% coid” degeneration.8 26 29–31 Occasionally, authors have reported “hyaline” 25 27 Stress degeneration, which is characterised by 1–3% hardness rather than the softness inherent in mucoid degeneration.1 Under light microscopy, the tendon of patients with jumper’s knee is characterised by 0–1% abnormal collagen, tenocytes, and vasculature. It does not consist of tight parallel collagen 321 45678 bundles but appears amorphous and disorgan- Strain (%) ised with collagen replaced by degenerative and necrotic tissue. Clefts in collagen suggest 30 20 microtearing. The characteristic reflective Figure 1 Stress-strain curve for tendon. Adapted from Leadbetter. polarised light appearance of normal collagen linear response to stress. Beyond this elonga- is lost.27 32 Alcianophilic ground substance,32 tion, tendon microfailures occur.1 Collagen consisting of glycosaminoglycans and fibres slide past one another as cross links fail.15 proteoglycans,33 is markedly increased. Teno- With even further strain, the tensile failure of cytes lose their fine spindle shape, and nuclei fibres themselves, combined with shear failure, appear more rounded.21 26 30 There is abnormal causes macroscopic damage in an unpredict- small vessel ingrowth.8263031 Very similar able fashion.15 histopathological changes occur in patients A force of 0.5 kN is experienced in level with Achilles tendinopathy.34 walking, and forces within the patellar tendon The presence of inflammatory cells in the may reach 8 kN during landing from a jump, excision biopsy samples from patients with up to 9 kN during fast running and 14.5 kN patellar tendinopathy is sometimes debated. during competitive weight-lifting (about 17 Two recent papers, coauthored by specialist times bodyweight).16–18 Basketball players jump pathologist authors who analysed all specimens on average 70 times per game, and the vertical in each study,27 32 reported the total absence of component of each ground reaction force in a inflammatory cells from tissue from patients jump is around six to eight body weights.19 with jumper’s knee, even at the periphery of Thus sports activities can impose stresses high abnormal tissue and in patients who had only enough to cause fibre failure. had symptoms for four months.32 Fibroblasts, however, were more plentiful than in the http://bjsm.bmj.com/ Patellar tendon pathology normal tendon,8 26 29–31 35–37 and these may have NOMENCLATURE FOR TENDON PATHOLOGY appeared to be inflammatory cells to earlier There is a lack of consistent nomenclature for authors. Papers reporting the presence of histopathological findings, and a standardised inflammatory cells have not mentioned stain- nomenclature has been proposed12021(table 2). ing methods or the expertise of the patholo- gist(s) reviewing specimens,25 28 38–40 and only 38 25 28 39 40 PATHOLOGY OF JUMPER’S KNEE one included a pathologist author. As recently as 1994, the pathology underlying This suggests that, in most cases, the on September 28, 2021 by guest. Protected copyright. patellar tendinopathy was not clearly defined,22 tendons of patients suVering patellar tendin- probably reflecting confusion arising from dif- opathy appear to have a tendinosis,32 a Table 2 Pathological classification of tendon disorders (from Clancy21) Pathological label Concept (macroscopic pathology) Histological finding Tendinosis Intratendinous degeneration (commonly due to aging, Non-inflammatory intratendinous microtrauma, vascular compromise) collagen degeneration with fibre disorientation, hypocellularity, scattered vascular ingrowth, occasional local necrosis or calcification Paratenonitis Inflammation of the outer layer of the tendon (paratenon) Inflammatory cells in the