Chapter 24
Anterior Knee Pain

with Jenny McConnell and Jill Cook

Patellofemoral instability

Patellofemoral instability or recurrent patellar subluxation is a variant of patellofemoral syndrome in which there is actual lateral subluxation of the patella rather than excessive lateral tracking. It is more common in females than males. Patients with patellofemoral instability complain of a sensation of the patella slipping or moving laterally on certain movements. When this occurs acutely, it may be associated with pain and swelling. This condition has the same predisposing factors as patellofemoral syndrome and the pattern of tenderness around the patella may be similar. Examination reveals patellar hypermobility with apprehension and pain when the patella is pushed laterally by the examiner. If there has been an acute episode there may be hemarthrosis or effusion. Patella alta (a patella that is located more superiorly than normal) and/or dysplasia of the femoral groove predispose to this condition.

Treatment of patellofemoral instability parallels that of the patellofemoral syndrome. Acute management aims to reduce pain and swelling. A brace may provide temporary immobilization and the patient may use crutches for either partial or nonweightbearing. Rehabilitation requires vastus medialis obliquus strengthening.

X-ray may reveal evidence of osteochondral damage to the articular surface of the patella and femur as well as any predisposing anatomical abnormalities, such as patella alta. Arthroscopy may be required to remove a loose osteochondral fragment.

Surgery is indicated if a properly managed conservative program fails. Arthroscopic lateral release and medial plication may be appropriate for a patient with recurrent patellar subluxation. Following surgery, an intensive rehabilitation program is vital.

Fat pad irritation/impingement

Fat pad syndrome was first described by Hoffa in 1903, to describe a condition where the infrapatellar fat pad was impinged between the patella and the femoral condyle, due to a direct blow to the knee. The condition can be extremely painful and debilitating, as the fat pad is one of the most pain sensitive structures in knee [8]. Chronic fat pad irritation is relatively common and often goes unrecognized by the clinician [30]. A recent study of college athletes found that 78% of those diagnosed with patellar tendinopathy over a 6 month period had increased signal in the fat pad on a T2 weighted MR image [31] (Figure 24.11) The pain is often exacerbated by extension maneuvers such as straight leg raises and prolonged standing, so it needs to be recognized early so appropriate management can be implemented.

Fig 24.11 
Taping the superior pole of the patella in 
the treatment of fat pad impingement. This 
elevates the inferior pole of the patella

Clinical findings involve localized tenderness and puffiness in the fat pad with the inferior pole of the patella being displaced posteriorly (Table 24.2). These patients often have hyperextension of the knees (genu recurvatum) associated with increased anterior pelvic tilt.

Treatment of the inferiorly tilted patella consists of taping across the superior surface of the patella in order to lever the inferior pole forward and relieve impingement of the fat pad (Fig. 24.12). Unloading of the fat pad may be required to relieve the symptoms further. The principle of unloading is based on the premise that inflamed soft tissue does not respond well to stretch. For example, if a patient presents with a sprained medial collateral ligament, applying a valgus stress to the knee will aggravate the condition, whereas a varus stress will decrease the symptoms. The same principle applies for patients with an inflamed fat pad. The inflamed tissue needs to be shortened or unloaded. To unload an inflamed fat pad, a 'V' tape is placed below the fat pad, with the point of the 'V' at the tibial tubercle coming wide to the medial and lateral joint lines. As the tape is being pulled towards the joint line, the skin is lifted towards the patella, thus shortening the fat pad (Figure 24.13). Muscle training and improving the lower limb mechanics are important components of the treatment of fat pad irritation. Surgery, where removal of part or all of the fat pad has been attempted, has had variable results.

Patellar tendinopathy

There have been many advances in understanding of the histopathology, imaging, and surgical outcomes in this condition in the past decade. Nevertheless, successful management of the jumping athlete with patellar tendinopathy remains a major challenge for the practitioner and patient.

Nomenclature

Patellar tendinopathy was first referred to as 'jumper's knee' due to its frequency in jumping sports (e.g. basketball, volleyball, high, long and triple jumps).. However, the condition also occurs in sports people who do not perform a lot of jumping. The term 'patellar tendinitis' is a misnomer, as the pathology underlying this condition is degenerative tendinosis rather than inflammatory 'tendinitis' (see below). Fortunately, the term patellar tendinitis is falling out of favor. On balance, patellar tendinopathy is probably the most appropriate general label for this condition (Chapter 2).

Pathology and pathogenesis of patellar tendinopathy

To the naked eye, the patellar tendon of patients undergoing surgery for patellar tendinopathy contains soft, yellow-brown tissue adjacent to the lower pole of the patella. This macroscopic appearance is commonly labeled as 'mucoid degeneration'. Under the light microscope, symptomatic patellar tendons do not consist of tight parallel collagen bundles but instead collagen fibers lose their continuity and are separated by a large amount of mucoid ground substance that gives them a disorganized and discontinuous appearance. Clefts in collagen and occasional necrotic fibers suggest microtearing. There is also small vessel ingrowth. This histopathological picture, which is called 'tendinosis', is identical in both tendons with macroscopically evident partial tears and those without. These regions of tendon degeneration correspond with areas of increased signal on MR imaging and hypoechoic regions on ultrasound.

Many cases of patellar tendinopathy co-exist with patellofemoral syndrome. Altered biomechanics of the patellofemoral joint may increase the mechanical strain on the tendon to cause injury. Alternatively, patellofemoral joint dysfunction may lead to decreased quadriceps strength, which also predisposes to patellar tendinopathy. On the other hand, pain and disuse associated with patellar tendinopathy may lead to poor vastus medialis obliquus function and altered patellofemoral joint biomechanics. Regardless of the cause, the patellofemoral joint requires a thorough assessment in patients presenting with patellar tendinopathy.

Clinical features

The clinical features of patellar tendinopathy have been outlined in Table 24.2. The patient complains of anterior knee pain aggravated by activities such as jumping, hopping and bounding. Pain is usually of gradual onset although, in some cases, the athlete notices an acute tearing sensation and this may correspond to a partial tear of the tendon (see Partial tendon tears, below). The most common site of tendinopathy is the deep attachment of the tendon to the inferior pole of the patella, although midsubstance and distal lesions are described.

The tendon is tender on palpation either at the inferior pole or in the body of the tendon. There is frequently associated thickening of the tendon and, in longstanding cases, scarred nodules or defects may be palpable. However, because the lesion is deep, these do not necessarily correlate with the severity of the lesion. The most effective position for palpation is shown in Figure 24.14. It is also important to assess any possible precipitating factors such as muscle tightness of the quadriceps and hamstring muscles, increased neural tension or abnormal biomechanics of the pelvis, patellofemoral joint or lower leg. Calf weakness is common in patients with patellar tendinopathy.

Fig 24.12
Position of palpatation of the patellar tendon. Pressure on 
the superior pole tilts the inferior pole, allowing 
more precise palpatation of the tendon origin.

It is important to reproduce the patient's pain on examination. In less severe cases, it may be necessary to perform a functional eccentric activity, such as a drop squat or hop, to reproduce the pain. These activities also load the patellofemoral joint. Taping to correct the patellofemoral joint followed by reassessment may help to differentiate between the two conditions, or at least indicate if the patellofemoral joint should also be treated.

Patellar tendinopathy has traditionally been graded from grade I to grade IV on the basis of pain and its relation to activity according to the Blazina scale (Table 24.5). Note that the activity guidelines are empirical - that is, they are an educated recommendation. They have never been tested or validated.

Table 24.5 Clinical grading of patellar tendinopathy and guidelines for activity

An alternative method of monitoring of clinical progress of patellar tendinopathy can be performed using the VISA scale (Table 24.6). This simple questionnaire takes less than 5 minutes to complete and once patients are familiar with it they will be able to complete most of it themselves.

Investigation

Ultrasound examination and MR imaging (Fig 24.15) are the investigations of choice in patellar tendinopathy although clinicians must appreciate that these imaging modalities do not have 100% sensitivity and specificity for the condition.

Treatment

Treatment of patellar tendinopathy requires patience and a multifaceted approach that is outlined in Table 24.7. It is essential that the practitioner and patient recognize that tendinopathy that has been present for months may require a considerable period of treatment associated with reduced activity before full recovery occurs (page 000 - referring to chapter 2 section on tendinopathies). Conservative management of patellar tendinopathy requires load reduction by correcting biomechanical errors, diligent cryotherapy, appropriate strengthening exercises and massage therapy. Surgery is rarely indicated.

Table 24.7 Overview of management of patellar tendinopathy

Relative load reduction: modified activity and biomechanical correction

There are numerous ways of reducing the load on the patellar tendon without resorting to complete immobilization. Relative rest means that the patient may be able to continue playing or training if it is possible to reduce the amount of jumping or sprinting, or the total weekly training hours.

Correcting biomechanics improves energy-absorbing capacity of the limb both at the affected musculoskeletal junction and at the hip and ankle. The ankle and calf are critical in absorbing the initial landing load transmitted to the knee. Biomechanical studies reveal that about 40% of landing energy is transmitted proximally. Thus, the calf complex must function well to absorb a major portion of this load. Compared with flat-foot landing, forefoot landing generates lower ground reaction forces and if this technique is combined with a large range of hip or knee flexion, vertical ground reaction forces can be reduced by a further 25%.

Biomechanical correction requires assessment of both anatomic, and functional, shortcomings. Anatomic variants that predispose to patellar tendinopathy are tabled (Table 24.8).

Table 24.8 Anatomical characteristics associated with patellar tendinopathy

There are numerous functional biomechanical abnormalities. Inflexibility of the hamstrings, iliotibial band, and calf muscles lead to functionally restricted knee and ankle range of motion and are likely to increase the load on the patellar tendon. Hamstring tightness (decreased sit and reach test) is associated with increased prevalence of patellar tendinopathy. Weakness of the gluteal, lower abdominal, quadriceps and calf muscles lead to fatigue and aberrant movement patterns that may alter forces acting on the knee and restrict range of motion during activity. Therefore, proximal and distal muscles also need assessment in patients with patellar tendinopathy.

Fig. 24.13 Imaging appearances in athletes with patellar tendinopathy.

(a) Ultrasound images showing normal tendon on the left, and the characteristic thickened tendon with regions of loss of echogenicity (arrowed) on the right. This appearance, although only mildly abnormal compared with some cases (e.g., 24.13b) already corresponds with the histopathology of tendon degeneration - tendinosis.	(b) Ultrasound appearance of a patellar tendon with greater morphologic (structural) abnormality. There is a clearly demarcated region of hypoechogenicity (seen as a black defect within the white echoes). This appearance may be asymptomatic and is certainly not, per se, an indication for surgery.	(c) MR imaging appearance of patellar tendinopathy - the key feature is the area of increased (bright) signal (arrowed). Symptoms do not correlate precisely with the severity of imaging appearances.

Cryotherapy 

Cryotherapy (e.g., ice) may decrease the extravasation of blood and protein from new capillaries found in tendinosis. It also decreases the metabolic rate of tendon. Both of these mechanisms may promote healing of patellar tendinopathy.

Strengthening

An effective strength program embraces the principles outlined in Table 24.9.

Commonly prescribed exercises are illustrated in Fig 24.16 (= 1/e Fig 22.13)

Table 24.9. Strengthening program for treatment of patellar tendinopathy.

When should strengthening begin?

Therapists often have concerns as to when, and how should they begin a strengthening program. Even athletes with the most severe cases of patellar tendinopathy should be able to begin some exercise, at the very least calf strength and isometric quadriceps work, in standing. On the other hand, the athlete that has not lost a lot of knee strength and bulk can progress quickly to the speed part of the program.

Both pain and the ability of the musculotendinous unit to do the work should guide the amount of strengthening to be done. If pain is a limiting factor, then the program must be modified so that the majority of the work occurs relatively pain free, and does not cause delayed symptoms, commonly pain the morning after exercise. A subjective clinical rating system, such as the VISA score (p. 000), will help both the therapist and the patient measure progress, and allow early detection of worsening symptoms.

If pain is under control, then it is essential to monitor the ability of the limb to complete the exercises with control and quality. Exercises should only be progressed if the previous work load is easily managed, pain is controlled, and function is satisfactory.

Athletes with patellar tendinopathy tend to 'unload' the affected limb to avoid pain, so they commonly have not only weakness, but also abnormal motor patterns which must be reversed. Strength training must graduate to single leg exercises (Figure 24.14, b, c), as the athlete can continue to unload the affected tendon when exercising using both legs. Thus, exercises that target the quadriceps specifically, such as leg extensions, may have a place in the rehabilitation of patellar tendinopathy. Similarly, when the athlete is ready, we increase the load on the quadriceps by having the patient stand on a thirty degree decline board to do squats. Compared with squatting on a flat surface, this reduces calf support during the squat.

Table 24.9 Strengthening program for treatment of patellar tendinopathy

The therapist should progress the regimen by adding load and speed, and then endurance to each of those factors. Combinations such as load and speed, or height and load then follow. These end-stage exercises, including eccentric programs can provoke tendon pain, and are only recommended after a prolonged rehabilitation period and when the sport demands intense loading. In several sports it may not be necessary to add potentially aggravating activities such as jump training to the rehabilitation program, whereas in volleyball, for example, it is vital.

Finally, the overall exercise program must correct aberrant motor patterns such as stiff landing mechanics (discussed above) and pelvic instability. For example, weight bearing exercises must be in a functionally required range and the pelvis position must be monitored and controlled at all times. Common errors in rehabilitation strength programs are tabled (Table 24.10).

Fig 24.14 Eccentric strengthening program - patellar tendon

(a) Double leg drop squats	(b) Single leg drop squats	(c) Single leg drop squats holding weights

Table 24.10 Common reasons why rehabilitation programs fail

Massage therapy 

Massage therapy is performed on the tendon to promote the repair process and to decrease adhesions between the tendon fibers. It should be low grade (I) in the acute stages. The most effective form of treatment in this condition is digital ischemic pressure followed by transverse friction throughout the entire tendon (Fig. 24.17). If tightness in the quadriceps muscle is present, sustained myofascial tension can be performed on the quadriceps muscle with the knee flexed.

Modalities

In laboratory studies, therapeutic ultrasound increased collagen synthesis in fibroblasts and increased tensile strength of tendon that had been surgically severed but had little effect on inflammation. Ultrasound had no significant effect on rat patellar tendon. There is no evidence in humans that modalities are a cost-effective therapy in tendinopathy.

Surgery 

Patellar tendon surgery has a rather unpredictable outcome as published success rates vary from 46-100%. Three large studies reported surgical success rates of 91%, 82% and 80% in 78, 80 and 138 subjects, respectively. The mean time to return to pre-injury level of sport varied from 4-9 months. A long-term outcome study of surgery for patellar tendinopathy found that only half the patients were able to return to previous level of sport. In two prospective studies evaluating time to return to sport it appeared that most subjects required in excess of 6 months, and often 9 months, to return to full sporting competition. There is no consensus as to the optimal surgical technique to use, with surgeons performing either a longitudinal or a transverse incision over the patellar tendon and generally excising abnormal tissue. Some surgeons excise the paratenon, while others suture it after having performed the longitudinal tenotomies and excision of the tendinopathic area. Arthroscopic debridement of the posterior portion of the patellar tendon has been described and results appear similar to that of open surgery.

Fig 24.15 Massage therapy 
 transverse friction of the patellar tendon

Recently, surgeons tested a less invasive approach to patellar tendon surgery - ultrasound guided multiple longitudinal tenotomy and reported 60% success and more rapid return to sport than surgery using the traditional methods. However, the authors recommend careful selection of patients, as this approach was more successful in patients with tendinopathy of the main body of the tendon, than in the more classic lesion near the proximal pole of the patella.

We recommend surgery only after a thorough, high-quality conservative program has failed. Surgeons must advise patients that while symptomatic benefit is very likely, return to sport at the previous level cannot be guaranteed (60-80% likelihood). Time to return to previous level of sport, if achieved, is likely to take between 6 and 12 months.