Chondral Lesions and Patellar Instability

Tan Si Heng Sharon

Hui James Hoi Po

INTRODUCTION

Pathogenesis

Patellar instability is the leading cause of cartilage damage in physically active children and adolescents, with up to 97% of chondral injury documented.¹,²,³,⁴,⁵,⁶,⁷,⁸,⁹
It may be secondary to macrotrauma or microtrauma.¹⁰
In acute dislocations, chondral lesions occur as a result of macrotrauma.⁸,⁹,¹⁰,¹¹,¹²
- Direct impact injury occurs during lateral patellar dislocation and reduction as the medial patella strikes against the lateral femoral condyle. This results in a shearing mechanism that causes patellar articular cartilage damage, in particular to the inferomedial patellar surface.
- Management of acute osteochondral or chondral fractures is discussed in Chapter 24.
Recurrent instability then causes subsequent ongoing chondral damage via microtrauma.³
- Abnormal joint loading and altered biomechanics create excessive contact stresses and shearing forces, leading to repetitive microtrauma and progressive cartilage wear.²,³,¹⁰,¹³
- Lateral patellar facet chondral lesions are often secondary to chronic patellar tilt and excessive lateral pressure syndrome, whereas medial patellar facet chondral lesions are often secondary to deficient contact or patellar dislocations.²,¹⁴
Chondral lesions of the patella and/or trochlea are frequently associated with patellar instability, alignment issues, or anatomic risk factors like trochlear dysplasia and patella alta. Thus, management of patellofemoral chondral lesions would include (besides treatment of chondral lesion) the evaluation and management of underlying or associated pathology.
This chapter would focus on management of focal or unipolar chondral lesions of patellofemoral joint. Management of bifocal, advanced chondral lesions, and generalized chondrosis/arthrosis of patellofemoral joint would be discussed in Chapter 26.

CLASSIFICATION

Includes focal chondral or osteochondral defects, osteochondral fractures or loose bodies in acute dislocations, and secondary diffuse degenerative changes in recurrent instability.³,¹⁵
Chondral defects are defined as partial-thickness defects without subchondral bone damage, whereas osteochondral defects are defined as full-thickness defects with underlying subchondral bone damage.⁷,⁹

SURGICAL ANATOMY

Majority of the lesions affect the patella, followed by the lateral femoral condyle.¹,²,³,⁷,¹⁶,¹⁷,¹⁸
- Patellar lesions
  - Small avulsion fractures from the medial rim of the patella are typically from its inferomedial aspect and corresponds to medial patellotibial ligament insertion.¹,²,³,⁷,¹⁹
  - Medial facet lesions were more commonly high grade, compared to low-grade lesions that were distributed throughout the cartilage surfaces.²
- Femoral lesions
  - Most commonly in the lateral femoral condyle or trochlea, though the weight-bearing surfaces of the lateral femoral condyle could also be affected.³
  - Less common than patellar lesions and frequently occur with patellar lesions.³,¹⁷
  - A full-thickness chondral lesion was more likely to be present when both patellar and lateral femoral condyle lesions were present, in view of the greater extent of shearing forces and contact stresses that resulted in both injuries.⁷
Acute dislocations have predominantly medial lesions, whereas recurrent instability had predominantly lateral lesions.²,³,¹⁴
Other sites of chondral injuries include the median ridge and lateral patellar facet, and the anterior third of the lateral femoral condyle and lateral trochlea.¹⁹

Figure 25.1 Axial and Sagittal magnetic resonance imaging demonstrating the presence of a patellar chondral lesion.
Underlying anatomic abnormalities could also predispose to different injury patterns.
- For example, patients with patella alta were associated with central patellar chondral injuries with higher grades. This is postulated to be caused by reduced stability of the patella within the trochlear groove, allowing it to be more vulnerable to shearing forces.²⁰ The predisposition of patella alta to patellar instability could also explain for inferior patellar lesions because only the inferior patella is engaged with the trochlea during the instability episodes.³

EVALUATION

Patient History

Similar to those of other patellofemoral problems.¹⁴
Typically present with anterior knee pain that is worst with climbing downstairs.¹⁰,¹⁴
- The presence or duration of anterior knee pain or crepitation, however, has been found to have poor correlation with the grading of lesions via magnetic resonance imaging or arthroscopy.¹⁴,¹⁷
Some patients would also present with a history of patellar dislocation or instability.¹⁰

Imaging

Radiographs have poor sensitivities and may be normal or may demonstrate osteochondral loss.³,¹⁴,¹⁷
Computed tomography also lacks sensitivity, though the use of arthrography increases the sensitivity that is similar to magnetic resonance imaging.³
Magnetic resonance imaging is the workhorse for the diagnosis ⁴,¹²,¹⁴ (Figure 25.1).
Particularly useful in preoperative and physical therapy planning to offload the injured chondral surfaces and to assess other predisposing factors for patellofemoral instability that could be addressed during the same surgery.¹⁸
Allows detection for both low and high-grade lesions, although the sensitivity for low-grade chondral lesions is significantly lower than that for high-grade lesions.¹²,¹⁴
Sizing, depth measurement, displacement analysis, grading, and assessment of subchondral injury could also be performed.¹⁰,¹⁴
Several imaging techniques, including arthrogram, T2 relaxation time mapping, delayed gadolinium-enhanced magnetic resonance imaging of cartilage, T1 rho, and sodium imaging, have been developed to enhance its sensitivity²,¹⁰,¹² (Figure 25.2).
These cartilage-specific magnetic resonance imaging sequencing can be used to evaluate cartilage repair tissue postoperatively.

Figure 25.2 Magnetic resonance imaging of a 14-year-old boy with patellar dislocation. Axial T2-weighted image and T2 relaxation time mapping demonstrate high-grade cartilage damage and increased T2 values in the medial and central areas of patellar cartilage. Compared to delayed gadolinium-enhanced magnetic resonance imaging of cartilage technique that is sensitive to the glycosaminoglycan content of cartilage, the T2 mapping is sensitive to the collagen network structure and content. T2 mapping obviates the need for contrast. Courtesy: Hee Kim, MD.

INDICATIONS AND CONTRAINDICATIONS

The goal of management of chondral lesion is to relieve pain and optimize cartilage restoration.¹⁶
- However, that is particularly challenging because of both intrinsic and extrinsic factors.
- Intrinsically, the articular cartilage lacks vascularization, rendering it incapable of repair.²¹,²²
  - Chondral lesions are, therefore, irreversible.¹⁴,²²
  - Osteochondral lesions, which involve the subchondral bone, would typically lead to fibrocartilage formation, which has inferior biomechanical properties and does not protect the subchondral bone from further degeneration.¹⁴
- Extrinsically, patients with patellar instability often have other anatomic abnormalities, such as malalignment, which predisposes the cartilage to continuous shear and forces.¹⁰,¹⁶
  - The general principle is then to offload the chondral lesions and restore patellofemoral biomechanics. Failure to address the predisposing factors of patellar instability has been known to lead to inferior outcomes of cartilage restoration.
Conservative management is usually the first-line management.¹⁰,¹¹
Failure of conservative management for symptomatic cartilage defects and cartilaginous lesions with subsequent patellofemoral osteoarthritis warrants surgical management.¹⁰,¹⁶,²¹,²³
- Specific indications for each procedure are discussed in Table 25.1.
Early surgical management is indicated for severe chondral lesions, large loose bodies or osteochondral fractures, irreducible patellar dislocations, focal medial patellofemoral ligament injuries, and recurrent patellar dislocations because these could lead to further chondral damage and osteoarthritis.³,¹¹,¹²,¹⁶,¹⁷
High-performance athletes would also benefit from early surgical management to optimize function.¹⁷

NONOPERATIVE MANAGEMENT

Includes physical therapy, taping, bracing, nonsteroidal anti-inflammatory drugs, and, occasionally, intra-articular corticosteroid injections or viscosupplementation.³,¹⁰
- Physical therapy should focus on quadriceps, pelvis, and core strengthening, as well as the restoration of proprioception and range of motion.
At least 6 months of conservative management is usually attempted, to allow the strength, balance, proprioception, flexibility, and motion of the patient to be optimized.¹⁰

SURGICAL MANAGEMENT

Overview

Could be subclassified into palliative, reparative, restorative, or reconstructive procedures.⁸,⁹,¹⁰,¹¹
- Palliative procedures include loose body removal or debridement to relieve mechanical symptoms.
- Reparative procedures include fixation of fracture fragments to repair the chondral defects.
- Restorative procedures include endogenous and exogenous cell therapy, namely, marrow stimulation, autologous chondrocyte implantation, or particulate juvenile cartilage, which aims to restore the chondral surface.
- Reconstructive procedures include autograft or allograft transplantation to fill the bone and chondral defect, or arthroplasty in severe cases.
These surgical procedures could be performed in isolation or in conjunction with other procedures. The specific details of other concomitant procedures could be found in their respective chapters, though their influence on chondral lesions is briefly discussed below.

Positioning

The patient is positioned supine on a standard operating table.
A well-padded thigh tourniquet is applied to the operative limb.
A side support is then placed at the level of the tourniquet, and a sand bag is placed at the foot to allow 90° knee flexion.
- The positioning of the side support should be checked that it does not impede:
  - Valgus and external rotation to allow access to the medial compartment
  - Figure of four positions to allow access to the lateral compartment
The operative limb is then prepared up to the level of the thigh tourniquet.

ARTHROSCOPIC APPROACH TO THE KNEE

Standard portals for diagnostic arthroscopy include the anterolateral and anteromedial portals.²⁴
The anterolateral portal is first placed.²⁴
- The landmark for the anterolateral portal is the soft spot created by the lateral border of the patellar tendon and the lateral joint space with the knee in 90° flexion.
- A transverse stab incision is placed approximately 1 to 1.5 cm above the joint line and deepened till there is a sudden decrease in resistance, indicating that the retinaculum has been incised.
- Withdraw the blade and then insert a straight artery for dissection.
- The arthroscopic sheath and trocar is then inserted with advancement of the arthroscopic sheath up into the suprapatellar pouch during knee extension.
- Remove the trocar once the arthroscopic sheath is positioned.
- The irrigation fluid is then connected and switched on prior to insertion of the arthroscope.
The anteromedial portal can then be placed in a similar manner to allow instrumentation.²⁴
- The landmark for the anteromedial portal is the soft spot created by the medial border of the patellar tendon and the medial joint space with the knee in 90° flexion.
The accessory medial portal can be used to access medial facet of the patella (Figure 25.3).

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