ANTERIOR KNEE PAIN

Q angle The direction of pull of the combined heads of all four parts of the quadriceps muscle produces a measure known as the Q angle. This is the angle between a line drawn from the anterior superior iliac spine through the centre of the patella and the intersection of a line from the centre of the patella to the tibial tubercle (see Figs. 3a and 3b). The average angle for men is 11 degrees and 15 degrees for women. Incorrect lower limb alignment will increase this angle considerably compare figure 3a with 3b. An increase in angle has a significant effect on patella tracking and the direction of forces, which are applied to the whole extensor mechanism.

Bony abnormalities An abnormal patella, either because it is too small, high or low riding within the trochlear groove will affect the way in which the patella tracks along the trochlear groove. Genu valgus and varum, femoral anteversion and tibial torsion will all increase the Q angle. Genu recurvatum (hyper-extended knees) has the potential to irri- tate the fat pads. All these abnormalities are usually fixed con- genital deformities, which can only be compensated for, not nec- essarily treated.

Foot posture Altered foot biomechanics (see SportEX Medicine Iss 4) such as excessive, prolonged or late foot pronation, will significantly affect tibial rotation at varying times during the gait cycle. Tibial rota- tion affects both the Q angle and patella tracking and torsional stresses at the knee. A greater degree of rearfoot varus has been found in AKP patients than normal subjects in a number of stud- ies, along with changes in the degree and timing of pronation (3). Changes in/or inappropriate, footwear could also have a negative effect on foot posture. Correction of foot postural problems can be achieved through the prescription of an appropriate orthotic device and the retraining of the antipronatory muscles of the foot.

Soft tissue length Short hamstrings decrease knee extension and increase knee flex- ion during running, this increases resistance to knee extension and therefore knee extensor moment and so loading on the patellofemoral joint. Gastrocnemuis/soleus tightness is associat- ed with a premature heel lift and foot pronation. A short iliotib-

applied to the tissues, as the body’s tissues are not as well adapted to accepting these loads, therefore tissue failure and injury can occur.

An example of lower limb alignment during a func- tional activity is shown in figures 3a and 3b. In fig- ure 3a the subject is carrying out a single leg squat. Notice the differences when comparing this to figure 3b where incorrect lower limb alignment is taking place during the squat. Figure 3b shows the lower limb in excessive lateral pelvic translation, internal femoral rotation, external tibial rotation and foot pronation. The net effect of the altered alignment at the knee is an increased rotation and medial transla- tion (abduction) of the knee. These changes can gen- erate abnormal forces in the tissues of the knee,

ial band (ITB) causes an increased internal femoral and external tibial rotation as the knee is extended, along with excessive ante- rior pelvic tilt and lateral displacement. All of these cause an increase in Q angle. The ITB also has a connection to the lateral border of the patella (deep lateral retinaculum); if this structure is tight there is an increased lateral patella glide, enhancing mal- tracking. Appropriate stretching of the shortened structures is obviously required to correct the influence of shortened tissue on lower limb alignment.

Muscle strength imbalances The role of vastus medialis oblique (VMO) in countering the later- al pull of the vastus lateralis has been much discussed in relation to AKP. The VMO is the only dynamic medial stabiliser of the patel- la, therefore if it is weak it cannot counter the lateral pull of the other quadriceps muscles leading to mal-tracking. Two reviews of this material are available (4,5), the conclusion from these reviews is that a balance needs to exist between all of the quadri- ceps group in order to allow normal tracking of the patella. It may prove that there is a critical level of quadriceps activation required for this proper tracking.

The ability to fully activate the gluteus medius muscle is crucial in achieving correct lower limb alignment. Gluteus medius con- trols hip abduction and internal rotation. If insufficient activation occurs then the lower limb drifts into increased hip adduction/internal rotation and the pelvis laterally displaces (see Fig.3b). This all significantly affects Q angle and torsion at the knee.

References 1. Hunter G. Specific soft tissue mobilisation in the management of soft tissue dysfunction. Manual Therapy 1998;3(1):2-11 2. Curwin D, Standish E. Tendonitis: its etiology and treatment. Health & Co. Lexington, USA, 1984 3. Callaghan M, Baltzopoulos V. Gait analysis in patients with anterior knee pain. Clinical Biomechanics 1994;9:79-84 4. Herrington L. The role of vastus medialis obliques in patellofemoral pain Critical Reviews in Physical and Rehabilitation Medicine 1998;10(3):257-263 5. Powers C. Rehabilitation of patellofemoral joint disorders: a critical review. Journal of Orthopaedic and Sports Physical Therapy 1998;28(5):345-35

Q angle

Figure 3b: Abnormal align- ment during a single leg squat

which could trigger AKP. The rotation could be expressed as a torsional load on the patella tendon or altered patella tracking. The increased abduction of the knee changes the angle of pull of the quadri- ceps altering patella tracking as it passes through the trochlear groove. Or causes the ITB to ‘bow- string’ across the lateral aspect of the knee joint. There is an intimate relationship between lower limb alignment and AKP because of the chronic overuse nature of the conditions, which cause AKP. It is therefore essential when a patient presents with AKP, not only to differentiate the structure involved in causing the pain, but also to assess for any biomechanical lower limb mal-alignment which could be the cause of the abnormal stress on the tissues leading to pain and injury.

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