Journal Logo

Intramedullary Insertion of the Patellar Tendon, a Rare Anatomical Variant, Its Sequelae, and Surgical Management

A Case Report

Collett, David J. BSc(Med), MBBS(Hons), MS1; Sharma, Rahul MBBS, DNB(Orth)2; Goyal, Prateek MBBS, Dip(Orth), DNB(Orth)3

doi: 10.2106/JBJS.CC.18.00397
Case Reports
Free
Disclosures

Case: We report a rare cause of patella baja in a 25-year-old man presenting with right knee pain. He was found to have patella baja and a genu recurvatum deformity. Imaging revealed an extremely unusual variant of the patellar tendon—identified to have an intramedullary tibial insertion. A patellar tendon reconstructive procedure was performed.

Conclusions: An intramedullary insertion of the patellar tendon is a fascinating and rare cause of patella baja with subsequent altered biomechanics of the extensor mechanism. We believe this is the first case report to describe its surgical presentation and an operative approach to its management.

1Department of Orthopaedic Surgery and Musculoskeletal Medicine, Macquarie University Hospital, NSW, Australia

2Department of Orthopaedic Surgery, Nepean Hospital, NSW, Australia

3Department of Orthopaedic Surgery, S.D.M.H Hospital, Jaipur, Rajasthan

E-mail address for D.J. Collett: davec1324@gmail.com

Investigation performed at Macquarie University Hospital, NSW, Australia and S.D.M.H Hospital, Jaipur, Rajasthan

Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSCC/A849).

Back to Top | Article Outline

Introduction

Patella baja refers to an abnormally low-lying patella relative to the femoral trochlea and can be associated with a clinical picture of restricted range of motion, crepitus, and retropatellar pain1,2. The etiology of patella baja can be divided into developmental, acquired, or a combination of the 2 and is most frequently encountered in post-total knee replacement patients3,4. Developmental causes of the condition are often seen as a component of more complex syndromes such as Osgood-Schlatter disease, Sinding-Larsen-Johansson syndrome, and patellar tendinitis3,5,6. Although the developmental form is present from an early age, the condition rarely causes significant symptoms until later in life where it may contribute to extensor dysfunction. Optimal management in such cases, with functional impairment or significant morbidity, is usually through surgical intervention with correction of the abnormal anatomy1,7.

Although its nomenclature merely describes a low-lying patella, the condition and its sequalae are far more complex with the altered anatomy resulting in significant changes to the usual biomechanics of the extensor mechanism. The low-lying patella will reduce the Q-angle and thus impair the ability of the extensor mechanism to resist external rotation of the tibia, producing abnormal pressures within the femoral-tibial joint7-11.

Various minor anatomical variations of the extensor mechanism and, in particular, the patellar tendon have been described12-15. However, only one other case report describing an intramedullary insertion of the patellar tendon was found after an extensive literature review. Beall et al. published a case report describing in detail the unusual radiographic findings of such an anomaly16.

We hope to add to the current understanding of such an unusual anatomical variant by describing a further case of this highly unusual anomaly, exploring its potential biomechanical effects and describing in detail our experience and approach to its surgical management.

The patient was informed that data concerning the case would be submitted for publication, and he provided consent.

Back to Top | Article Outline

Case Report

Presentation

A 25-year-old man presented with right knee pain and hyperextension. The pain was described to be of an intermittent nature, worse on exertion and terminal flexion. No associated swelling, effusion, or erythema was described. He denied any history of trauma or infective symptoms, with no indication of systemic pathology. The patient had no other significant medical or surgical history, with no previous trauma to the knee. Furthermore, there was no family history of any osseous or congenital disorders and no social or occupational history, which would point to a likely cause of his pain.

Systemic examination was unremarkable without obvious bone disorder. Focused examination of the knee revealed a genu recurvatum deformity with pain on terminal flexion (Fig. 1). Active motion was found to range from −10° to 120°, with a passive range of motion of −10° to 140°. No tibial tuberosity was palpable with mild tenderness over this region. The remainder of the knee examination was found to be unremarkable, without instability, effusion, or ligament laxity.

Fig. 1

Fig. 1

Back to Top | Article Outline

Imaging

Lateral X-rays taken in 30° of flexion revealed a significant patella baja deformity with a Caton-Deschamps index of 0.15 (normal range 0.6-1.2) and Blumensaat line passing through the upper third of the patella (Figs. 2 and 3)17,18. It was further noted that no definitive tibial tuberosity could be identified with evidence of tunneling of the tibial metaphysis seen on the lateral view (Fig. 3).

Fig. 2

Fig. 2

Fig. 3

Fig. 3

Images obtained through magnetic resonance imaging (MRI) were significantly abnormal, revealing what appeared to be an extension of the patellar tendon through the anterior cortex of the tibia, into the medullary canal, and attaching to the internal wall of the posterior cortex. Abnormal hyperintense signal intensity was seen surrounding the patellar tendon insertion suggestive of edema due to increased strain (Fig. 4).

Fig. 4

Fig. 4

A subsequent computed tomography (CT) scan was obtained to better visualize the details of this highly unusual anatomical variant (Figs. 5 and 6). A significant deformity of the proximal tibial cortex was noted with an anterior oval-shaped foramen allowing entry of the patellar tendon into the medullary canal and its insertion onto the posterior cortex (Fig. 7). Complete absence of the tibial tuberosity was again noted.

Fig. 5

Fig. 5

Fig. 6

Fig. 6

Fig. 7

Fig. 7

The articular cartilage was found to be normal on both the CT and MRI scan; hence, no arthroscopy was performed.

Back to Top | Article Outline

Intraoperative Findings and Reconstruction

An anterior approach to the patella, patellar tendon, and proximal tibia was performed. A midline incision was made through the skin and subcutaneous tissues. The patellar tendon was meticulously dissected and found to extend from the inferior pole of the patella through an intraosseous tunnel into the medullary canal of the proximal tibia. No tibial tuberosity was identified, instead replaced by a trough-shaped canal running into the osseous foramen. The patellar tendon was found to extend into the medullary canal where it inserted onto the internal surface of the posterior cortex through what appeared to be a fibrous hypertrophied enthesis. The patellar tendon was subsequently released at its distal aspect and transferred proximally. The patellar tendon insertion was repositioned to correct the patella baja deformity and fixed to an area of the anterior tibia deemed to approximate the location of the deficient tibial tuberosity. Dual fixation of the tendon to the anterior tibia was achieved using a screw and spiked washer and intrasubstance braided ethibond cross-stitches (Fig. 8). The subcutaneous tissue and skin were subsequently closed in layers.

Fig. 8

Fig. 8

Back to Top | Article Outline

Postoperative Course

The postoperative phase was uneventful, with timely wound healing, well-controlled pain, and a gradual return to function. The patient was kept from weight bearing for 2 weeks, followed by gradual flexion and isometric quadriceps exercises—guided by physiotherapy. The patient was subsequently reviewed in clinic at 6 weeks, 3 months, and 2 years. At his most recent assessment, the patient had no pain, no hyperextension or extensor lag, normal range of motion from 0° to 140° (active and passive), and a complete return to normal functional activities (Fig. 9). Postoperative lateral radiographs of the knee in 30° of flexion revealed a complete correction of the patella baja deformity—with a Caton-Deschamps index of 0.84 (normal range 0.6-1.2) (Fig. 10).

Fig. 9

Fig. 9

Fig. 10

Fig. 10

Back to Top | Article Outline

Discussion

Anatomical abnormalities of the extensor mechanism are uncommon, and those that are encountered are usually minor with little clinical significance. However, as profoundly illustrated by this case, significant anomalies can and do arise and are unlikely to conform to conventional diagnosis. Their mechanical and clinical effects can be complex, and management requires ingenuity and a sound understanding of the delicate biomechanics of the extensor mechanism of the knee.

Kasten et al. describe a number of cases of patellar tendon aplasia and their attempts at reconstruction, whereas Loizides et al. describe a case of a crossed-doubled patellar tendon incidentally found during a knee MRI scan12,14. Tyler et al. have described a number of other interesting and uncommon variants of the extensor mechanism with a focus toward diagnostic imaging13. Cases of developmental patella baja have also been described in association with a number of clinical syndromes including Osgood-Schlatter disease, Sinding-Larsen-Johansson syndrome, and patellar tendinitis3,5,6.

Only a single other case report involving an intramedullary insertion of the patellar tendon has been described. Beall et al. discuss the radiological findings of such an anomaly in an 8-year-old girl. Interestingly, many similarities can be drawn between the 2 cases, with an almost identical clinical presentation. Both patients were found to have a significant patellar baja and genu recurvatum deformity with symptoms of instability and patellofemoral pain16.

The major biomechanical effects of the anatomical anomaly are derived from the lengthened patellar tendon and its altered insertion, distal and posterior to the extension-flexion axis of the knee. We hypothesize that both these effects will increase the lever arm of the extensor mechanism and increase the excursion of the knee joint, resulting in hyperextension and subsequent genu recurvatum—however, further mechanical analysis is required (Fig. 11).

Fig. 11

Fig. 11

The associated patella baja will reduce the Q-angle of the extensor mechanism and subsequently alter the transmission of forces across the knee joint (Fig. 12). Increased compressive forces across the articulation will likely result in abnormal pressure on the articular cartilage, especially nearing complete extension, which in time may contribute to arthritis and wear19.

Fig. 12

Fig. 12

Our reconstructive approach was aimed at modifying the unusual anatomy to restore the appropriate functional biomechanics of the extensor mechanism, and in many ways mimics and achieves the same outcomes as a tibial tubercle transfer and proximalization procedure20. By relocating the patellar tendon insertion, we have restored patella height, “normal” joint biomechanics, and patellar tracking, subsequently reducing the forces transmitted across the patellofemoral articulation2,21-23.

Given its scarcity, we feel that this case is not only fascinating to those with an interest in musculoskeletal pathology, but provides further insights into the anatomical and biomechanical complexity of the extensor mechanism and the effects such anatomical variants may have. Furthermore, we hope that this case will help to provide a frame of reference, and some guidance, to a possible management approach when faced with such unusual and fascinating anomalies.

Note: The authors acknowledge Ayeesha McComb for her work in the design and generation of the illustrations for this article and Dr John Read for his assistance with radiological interpretation and reporting.

Back to Top | Article Outline

References

1. Grelsamer R. Patella baja after total knee arthroplasty: is it really patella baja? J Arthroplasty. 2002;17(1):66-9.
2. Colvin A, West R. Patellar instability. J Bone Joint Surg Am. 2008;90:2751-62.
3. Chonko D, Lombardi A, Berend K. Patella baja and total knee arthroplasty (TKA): etiology, diagnosis, and management. Surg Technol Int. 2004;12:231-8.
4. Weale A, Murray D, Newman J, Ackroyd C. The length of the patellar tendon after unicompartmental and total knee replacement. J Bone Joint Surg Br. 1999;81:790-5.
5. Lancourt J, Cristini J. Patella alta and patella infera: their etiological role in patellar dislocation, chondromalacia and apophysitis of the tibial tubercle. J Bone Joint Surg Am. 1975;57:1112-5.
6. Medlar R, Lyne E. Sinding-Larsen-Johansson disease. Its etiology and natural history. J Bone Jt Surg Am. 1978;60(8):1113-6.
7. Sherman S, Erickson B, Cvetanovich G, Chalmers PN, Farr J, Bach BR, Cole BJ. Tibial tuberosity osteotomy: indications, techniques, and outcomes. Am J Sports Med. 2014;42(8):2006-17.
8. Lewallen D, Riegger C, Myers E, Hayes W. Effects of retinacular release and tibial tubercle elevation in patellofemoral degenerative joint disease. J Orthop Res. 1990;8(6):856-62.
9. Maquet P. Advancement of the tibial tuberosity. Clin Orthop Relat Res. 1976;115:225-30.
10. Singerman R, Davy D, Goldberg V. Effects of patella alta and infera on patellofemoral contact forces. J Biomech. 1989;27:1059-65.
11. Grelsamer R. Patellar malalignment. J Bone Joint Surg Am. 2000;82(11):1639-50.
12. Loizides A, Messina C, Glodny B, Gruber L, Brenner E, Gruber H, Henninger B. A case of crossed-doubled patellar tendon: an atavistic variant, simple mutation or pathological finding? Surg Radiol Anat. 2017;39(1):111-4.
13. Tyler P, Datir A, Saifuddin A. Magnetic resonance imaging of anatomical variations in the knee. Part 2: miscellaneous. Skeletal Radiol. 2010;39:1175-86.
14. Kasten P, Weiss S, Carstens C, Thomsen M. Failed surgical reconstruction of patellar tendon aplasia: a report of two cases. J Bone Joint Surg Am. 2005;87:2091-6.
15. Doral M, Atay A, Bozkurt M, Ayvaz M, Tetik O, Leblebicioglu G. Three-bundle popliteus tendon: a nonsymptomatic anatomical variation. Knee. 2006;13:342-3.
16. Beall D, Ponder C, Kirby A, Fish J. Intramedullary insertion of the patellar tendon. Skeletal Radiol. 2006;35(2):122-5.
17. Blumensaat C. Die Lagaebweichungen und verrenkungen der kniescheibe [in German]. Ergebn Chir Orthop. 1938;31:149-223.
18. Linclau L. Measurement of patellar height. Acta Orthop Belg. 1984;50:70-4.
19. Yang J, Fulkerson J, Obopilwe E, Voss A, Divenere J, Mazzocca AD, Edgar CM. Patellofemoral contact pressures after patellar distalization: a biomechanical study. Arthroscopy. 2017;33(11):2038-44.
20. Drexler M, Dwyer T, Marmor M, Sternheim A, Cameron H, Cameron J. The treatment of acquired patella baja with proximalize the tibial tuberosity. Knee Surg Sports Traumatol Arthrosc. 2013;21(11):2578-83.
21. Paulos L, Rosenberg T, Drawbert J, Manning J, Abbott P. Infrapatellar contracture syndrome: an unrecognized cause of knee stiffness with patella entrapment and patella infera. Am J Sports Med. 1987;15(4):331-41.
22. Paulos L, Wnorowski D, Greenwald A. Infrapatellar contracture syndrome: diagnosis, treatment, and long-term follow-up. Am J Sports Med. 1994;22:440-9.
23. Vandeputte F, Vandenneucker H. Proximalisation of the tibial tubercle gives a good outcome in patients undergoing revision total knee arthroplasty who have pseudo patella baja. Bone Joint J. 2017;99-B(7):912-6.

Supplemental Digital Content

Back to Top | Article Outline
Copyright © 2019 by The Journal of Bone and Joint Surgery, Incorporated