Published 10/1/2007
Elizabeth A. Arendt, MD

Putting a little sex in your orthopaedic practice

Are patellofemoral disorders worse for females?

Patellofemoral (PF) injury and disease are commonly thought to be more prevalent in females. Literature to support this conclusion, however, is inadequate. This article investigates possible sex differences in three categories of PF disorders: PF pain, PF instability, and isolated PF arthritis.

Patellofemoral pain
PF pain is dull and aching, typically located in the anterior knee. Patients with PF pain feel discomfort when engaging in such activities as going up and down stairs, kneeling, squatting, or sitting for extended periods with a bent knee. The causes of PF pain, which is common in athletic people (including runners) as well as sedentary individuals, are not well understood.

The older term, “chondromalacia patellae,” or softening of the cartilage, was used when pain was thought to be due to cartilage softening noted by gross inspection. More recently, however, PF pain has been attributed to some form of PF malalignment (static or dynamic), or an overuse mechanism, in which the patient is outside an “envelope” of function, resulting in pain.

A longitudinal study by Nimon and associates between 1974 and 1980 of 63 females with PF pain showed that 50 percent of the 54 participants who responded to the survey showed improvements during the first 4 years of the study.1 A follow-up study of 49 of these patients 12 years later showed an additional 23 participants had improved. The study also suggested that a subset of PF pain is not related to known structural disease indicated by standard physical exams and x-rays.

A separate group of researchers investigated constitutional features such as sex, age, body composition, athletic activity, and duration of symptoms. This study did not show sex as a determinant for PF pain. Age was the only predictive factor for favorable outcomes; younger patients did better.2

More recently, a 2-year prospective study evaluated physical education students with no prior history of knee problems on motor performance, joint laxity, alignment of the lower leg, muscle flexibility, and structure.3 Participants also received a physical exam for signs of PF disorders. Of the 282 students assessed (151 boys and 131 girls; average age, 18.6 years), PF pain developed in 7 percent of the males and 10 percent of the females. The study also identified a hypermobile patella and shortened quadriceps muscle as risk factors for pain.

An established link exists between PF pain and clinical overload. But how does muscle control and strengthening reduce PF pain? Although little is known about how the body restores normal neuromuscular control, improving strength and body control has been shown to reduce pain.

Neuromuscular differences exist between males and females;4 women typically have less muscle mass and different compositions of muscle fibers. Because testosterone, as well as increased physical activity levels, increases muscle mass, males may have an advantage in regard to knee stability. Studies have shown dimorphism in specific muscles in the body and differences in muscle fiber composition.5,6 Muscle stability also shows variances between the sexes; joint load is influenced by muscle strength and fatigue.

After puberty, male and female sex hormones play a significant role in determining the size and shape of soft-tissue structures that support the knee. These neuromuscular differences between males and females may explain discrepancies in the rates of PF pain and injury.7 Another consideration is pain perception; females are more sensitive to pain and have different physical responses to pain than males.8

Patellofemoral dislocations
PF dislocations are traumatic disruptions to patellar tracking. Studies have shown that, although acute patellar dislocations are more common in males, females may experience more recurrent dislocations. PF dislocation was the most prevalent injury among females 10 to17 years old, according to one study.9

Several physical features attributed to PF dislocation are more common in females. The female knee has a greater Q angle, a measurement reflecting the effect of the quadriceps on the knee. Females are more likely to have increased femoral anteversion, which can cause the limb to rotate inward, and they are more likely to have patella alta, a measurement of the distance between the kneecap and the knee joint. When the kneecap is in a higher position, the knee requires a greater degree of flexion before the the trochlear groove and its soft-tissue tension stabilize the kneecap.

A significant study by Dejour et al in 1994 analyzed anatomic factors of instability using radiographic imaging.10 Their study group was composed of 143 knees (59 percent female) with symptoms of patellar instability, 67 contralateral asymptomatic knees, and 190 control knee x-rays and 27 control knee computed tomography (CT) scans. The following relevant factors were noted in knees with symptomatic patellar instability:

  • Trochlear dysplasia and the presence of a trochlear bump
  • Quadriceps dysplasia, defined as lateral patellar tilt on CT scans
  • Patella alta
  • Tibial tuberosity-trochlear groove distance, defined as a measurement of distance between the two sites on the CT scan

The literature suggests that females have higher instances of certain dysplastic features that are risk factors for patellar instability. Although a sex disparity among first-time PF dislocations is debatable, females have more recurring PF dislocations. Understanding neuromuscular risk factors and their possible gender tendencies is key; joint morphology is a strong risk factor for injury.

Patellofemoral Arthritis
PF arthritis can be caused by chronic joint injuries, increasing age, weight, or overuse. Isolated PF arthritis is found in females more than twice as frequently as in males. A 1992 study by McAlindon et al examined the instance of PF arthritis diagnosed by radiographs in 273 patients with knee pain and 240 controls; 24percent of women and 11percent of men were diagnosed with PF arthritis.11

A recent multicenter study from France supports this theory.12 Of 578 PF arthritis patients, 72 percent were females. The study aimed to clarify the history of the disease. In 49 percent of the cases, the PF arthritis was idiopathic; 33 percent of patients had signs of objective patellar instability; 9 percent of patients had a previous history of blunt trauma, and 8 percent of patients had chondral calcinosis. One third of these patients had radiographic evidence of one or more dysplastic features of the PF joint, which are more common in females.

Do consider sex disparities when treating patients. Men’s bodies and women’s bodies are structured differently and have different physical reactions to clinical load. Although PF injuries and disease are often difficult to characterize and define, clinical data do support that PF problems are more common in females. Both anatomic and neuromuscular risk factors for PF disease and injury show sex variances.

Elizabeth Arendt, MD, is a professor of orthopaedic surgery and vice chair, department of orthopaedic surgery, sports medicine & knee arthroplasty at the University of Minnesota. She can be contacted at arend001@umn.edu


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