Knee, Ankle, and Foot Pain

Jesse Goitia, MD

Kevin Burnham, MD

FAST FACTS

Osteoarthritis of the knee is the most common cause of disability in the elderly.
Pain in the foot and ankle affects 1 in 5 adults 58 years and older.
Stroke should be included in the differential for a patient with acute lower extremity weakness or loss of sensation.
Diabetic neuropathy and ischemia-related nerve damage in peripheral artery disease results in lower limb pain.

INTRODUCTION

Lower extremity pain is a common patient encounter in primary care.¹ The prevalence of knee pain is estimated to be as high as 20% in the general population of adults and can be associated with significant disability.² Similarly, pain in the foot and ankle affects approximately 1 in 5 adults 58 years and older.³ In this chapter, we will discuss important causes of pain at, or around, the knee, leg, ankle, and foot. Pain associated with hip pathology will be discussed separately.

HISTORY

An accurate history can help a physician to focus the physical examination appropriately and guides the diagnostic process.⁴ The goal of the clinical interview should be to characterize the chief complaint, evaluate the impact on patient function, and attempt to establish a cause.⁵ Key elements of the history include localizing the area of pain, exploring the characteristics of the pain, defining the time course, inquiring about any recent trauma or prior interventions, exploring associated symptoms, and uncovering the mechanism of injury⁵^,⁶^,⁷ (Table 21-1).

MECHANISM OF INJURY

Having a clear understanding of the mechanism by which an injury took place increases the ability to make an accurate diagnosis. A thorough description of the mechanism of injury must account for the events leading to the injury and a description of the body/joint biomechanics at the time of injury. This description should include information regarding the environment where the injury took place, physical characteristics of the patient, the involvement of any forces external to the patient, including direct blows to the patient’s body and the presence of accelerating or decelerating forces.⁴⁶

Classically, anterior cruciate ligament (ACL) injuries are described as a twisting injury of the knee that is accompanied by an audible pop and rapid swelling of the knee joint.⁴⁷ It is also helpful to note if the injury occurred with acceleration or deceleration, a directional change, presence or absence of joint loading, a varus or valgus force through the joint, and the degree of knee extension.⁴⁸ It is valuable to understand that, in overuse injuries, the inciting injury may not be a single memorable event the patient will be able to recall.

TABLE 21-1 Differential Diagnosis by Timing

ACUTE/ABRUPT	CHRONIC/INSIDIOUS
Knee
ACL rupture⁸
Baker cyst, rupture causes acute pain⁹	Baker cyst⁹
Dislocations¹⁰
Hamstring tendonitis¹¹	Hamstring tendonitis¹¹
Medial plica syndrome¹²	IT band syndrome¹³
Meniscal tear¹⁴	Meniscal tear¹⁴
Monoarthritis (septic arthritis, gout, pseudogout, or inflammatory arthritis)^{15 ,16}
Patellar fracture^{17 ,18}	Patellar tendinopathy¹⁹
Patellar tendon rupture^{20 ,21}	Patellofemoral pain syndrome²²
Pes anserine bursitis²³	Pes anserine bursitis²³
Prepatellar bursitis²⁴	Prepatellar bursitis²⁵
Quadriceps tendon rupture²¹
Lower Leg
Baker cyst, rupture causes acute pain⁹	Chronic exertional compartment syndrome²⁶
DVT²⁷	DVT²⁷
Maisonneuve fracture²⁸	Medial tibial stress syndrome²⁹
	Popliteal artery entrapment syndrome³⁰
	Tibial bone stress injuries²⁹
Ankle and Foot
Achilles tendon rupture³¹	Achilles tendinopathy³²
Acute compartment syndrome³³
Ankle sprain³⁴
Calcaneal stress fracture³⁵	Calcaneal stress fracture³⁵
First MTP joint sprain³⁶
Metatarsal fractures³⁷	Metatarsal fractures³⁷
Os trigonum (posterior impingement)^{38 ,39}	Os trigonum (posterior impingement)^{38 ,39}
Plantar fasciitis⁴⁰	Plantar fasciitis⁴⁰
Sinus tarsi syndrome⁴¹	Sinus tarsi syndrome⁴¹
Stress fractures⁴²	Stress fractures⁴²
Syndesmotic (“high”) ankle sprain⁴³
Tarsal tunnel syndrome⁴⁴	Tarsal tunnel syndrome⁴⁵
IT, iliotibial; MTP, metatarsophalangeal.

LOCATION

Musculoskeletal pain may be well localized, occur in a particular anatomical region, or be widespread.⁴⁹ The localization of pain is often poor in deep-tissue structures, and it can be difficult to differentiate pain from bones, muscles, tendons, or ligaments.⁴⁹ For the knee, determining the general region from which pain is arising (anterior, medial, lateral, or posterior) can be useful when establishing a differential diagnosis.¹² For example, anterior knee pain may be suggestive of patellar or patellofemoral pathology, whereas medial knee pain may be more suggestive of meniscal or degenerative joint disease.¹²

Similarly, the location of pain within the foot and ankle can help formulate a differential diagnosis.⁵⁰ Pain in the rear foot could be brought on by Achilles tendon injury, plantar fasciitis, calcaneal stress fracture, heel contusion, or posterior tibial tendinopathy.⁴⁰ Pain along the medial aspect of the mid-foot may be a symptom of tarsal tunnel syndrome, whereas pain at the lateral mid-foot may be brought about by sinus tarsi syndrome.⁵¹

ALLEVIATING AND EXACERBATING FACTORS

Assessment of aggravating and alleviating factors aids diagnosis and development of a management strategy⁵²^,⁵³ (Table 21-2). Patellofemoral pain is described as a diffuse, aching anterior knee pain, without clear inciting injury.²²^,⁵⁹ There may be mechanical symptoms, such as the knee catching or popping while walking, but not locking of the knee.²²^,⁵⁹ Swelling is uncommon but may be reported along with stiffness.²² Patellofemoral pain is exacerbated by activities that increase stress on the patellofemoral joint, such as prolonged knee flexion (“theater sign”), walking down stairs, squatting, running, or jumping.²²^,⁵⁹ Always ask about recent changes in physical activity that could cause repetitive overload at the patellofemoral joint, particularly exercise routines.²²^,⁵⁹ Pain from pes anserine bursitis is exacerbated by going up and down stairs and is worse in the morning.⁶⁵ Meniscus pain is worse on torsional knee movements during weight bearing, such as pivoting about the knee while walking or running.⁶⁶ Plantar fasciitis is a common cause of heel pain in adult primary care setting. Pain is believed to be due to microtears at the calcaneal enthesis caused by biomechanical overuse from prolonged standing or running. Patients typically report heel pain and tightness on rising from bed in the morning or

after prolonged sitting. The pain typically improves with ambulation but can intensify toward the end of the day if patients had been on their feet most of the time.⁴⁰

TABLE 21-2 Alleviating and Exacerbating Factors of Painful Lower Extremity Conditions

	EXACERBATING	ALLEVIATING
Knee
Baker cyst	End-range knee extension⁵⁴
Hamstring tendonitis	Repetitive activities with the leg or hamstrings, including running, cycling, or stairs Sudden knee flexion¹¹
IT band syndrome	Running downhill Increasing stride length Prolonged knee flexion, such as sitting⁵⁵
Medial plica syndrome	Walking up or down stairs Squatting Rising from a chair after prolonged sitting⁵⁶
Meniscal tear	Walking Standing Twisting motions Nighttime⁵⁷
Patellar tendinopathy	Repetitive activities with the leg or quadriceps Prolonged sitting or squatting⁵⁸	Pain may improve after a certain “warm-up” period⁵⁸
Patellofemoral pain syndrome	Prolonged sitting Walking down stairs Squatting Running Jumping^{22 ,59}
Pes anserine bursitis	Walking up or down stairs²³ Repetitive flexion and extension¹²
Prepatellar bursitis	Direct pressure over the bursa End-range knee flexion⁶⁰
Septic arthritis	Range of motion, particularly flexion¹⁵
Lower Leg
Chronic exertional compartment syndrome	Pain increases in relation to intensity or duration of exertion²⁶	Rest²⁶
Medial tibial stress syndrome	Pain at the start of activity or exercise²⁶
Ankle and Foot
Achilles tendinopathy	Pain at the start of exercise⁶¹ Running Jumping
First MTP joint sprain	First MTP motion, particularly with walking or running⁶²
Morton neuroma	Ambulation Footwear with narrow toe box⁶³	Rest⁶³ Wide toe-box footwear
Os trigonum	Running downhill End-range ankle dorsiflexion³⁸
Plantar fasciitis	Weight bearing immediately out of bed or after prolonged rest⁴⁰ Prolonged walking or standing⁴⁰	Moderate ambulation typically improves pain⁴⁰
Sinus tarsi syndrome	Running or sprinting Stepping off a curb or walking on uneven ground may worsen the sensation of instability⁴¹
Tarsal tunnel syndrome	Prolonged sitting or standing⁶⁴ Nighttime symptoms are commonly reported⁶⁴	Rest and leg elevation⁶⁴
IT, iliotibial; MTP, metatarsophalangeal.

NEUROLOGIC SYMPTOMS

Damage to nerve tissue of the lower extremities is not uncommon and can lead to poor functional outcomes.⁶⁷ Symptoms of nerve injury include pain, loss of motor function, loss of sensation, and abnormal sensations.⁶⁸ Stroke should be included in the differential for a patient with acute lower extremity weakness or loss of sensation.⁶⁹ Other possible nonmechanical causes of lower extremity neurologic symptoms include diabetic neuropathy and ischemia-related nerve damage in peripheral artery disease.⁷⁰^,⁷¹

Trauma is an obvious example of an acute cause of lower extremity neurologic symptoms. For instance, traumatic dislocation of the knee can cause damage to the local neurovascular structures, particularly the tibial or peroneal nerve, which can lead to chronic pain and progressive weakness.⁷² Common peroneal nerve injury impairs dorsiflexion and eversion of the foot.⁷³ Absence of the ability to dorsiflex the foot results in foot drop, and unopposed inversion of the foot exacerbates this by making it even more difficult for a patient to clear their toes from hitting the ground during the swing phase of walking.⁷³ Deep peroneal nerve entrapment results in impairment of foot dorsiflexion and toe extension.⁷⁴ Superficial peroneal nerve damage affects ankle eversion.⁷⁴

Morton neuroma is a common cause of chronic foot pain. It is actually proliferative fibrosis of perineural tissue rather than a true nerve tumor. The underlying cause is not clear. Patients classically report a burning pain at the plantar aspect of the foot, between the third and fourth metatarsal heads. The pain may radiate to the toes and be associated with paresthesias. Walking in high heels or in shoes with a narrow toe box exacerbates the pain. The pain may be relieved with a change in footwear or foot massage.⁷⁵

ASSOCIATED SYMPTOMS

Inquiring about the related symptoms and features associated with a patient’s pain can be crucial in deriving a diagnosis. A patient with pain due to meniscal damage may describe insidious knee pain without identifiable injury that is associated with mechanical symptoms such as painful clicking, locking, and painless giving way.⁷⁶ Medial tibial stress syndrome is a common cause of exertional leg pain, particularly in runners, and is often described as absent at rest and subsiding after a period of continued exertion.²⁶ In contrast, pain due to a tibial stress fracture is more likely to be associated with increasing intensity with exertion and, possibly, pain at rest.²⁶ Another cause of exertional lower extremity pain is chronic exertional compartment syndrome. This disorder is often characterized as a cramping sensation that can affect any of the lower leg compartments and can be associated with numbness, weakness, and paresthesias.²⁶ An Achilles tendon rupture is associated with weakness, unsteady gait, limping, and difficulty climbing a step.⁷⁷

PRIOR DIAGNOSTIC STUDIES AND THERAPEUTIC INTERVENTIONS

Musculoskeletal imaging can be a powerful diagnostic tool for a wide variety of conditions. Review of prior images can provide a great deal of insight into a patient’s existing injury that history and examination may not be able to provide.⁷⁸ It is important to know about past treatments a patient may have received, not only to document efficacy but also to recognize the possibility of additional pathology brought about by those interventions.⁷⁹ For instance, the Achilles tendon is vulnerable to rupture following corticosteroid injection; knowledge of prior injections may raise suspicion for rupture in a patient presenting with rear-foot and ankle pathology.⁸⁰ In fact, patients may be at risk for tendon rupture even without a history of local steroid injections.⁷⁹ Systemic corticosteroid use can also place a person at risk for Achilles rupture, as can a history of fluoroquinolone use.⁷⁹^,⁸¹

The history of prior surgical interventions is similarly essential when evaluating a patient. For instance, patients with a history of ACL repair are at increased risk of graft rupture within the first 5 years following surgery, compared with individuals with no history of reconstruction.⁸²

Consider obtaining a physical medicine and rehabilitation consult when treating musculoskeletal injuries that do not improve with simple conservative measures such as rest, ice, compression, and elevation. Surgical referrals are necessary depending on the diagnosis; appropriate referral time is further delineated in Table 21-3.

TABLE 21-3 Examination and Management of Painful Lower Extremity Conditions

	EXAMINATION	WORKUP	TREATMENT	WHEN TO REFER
MSK
ACL injury	Hemarthrosis likely present. May be unable to fully extend knee. Lachman, anterior drawer, and pivot shift tests are the most accurate⁸	MRI is study of choice⁸	Conservative if no major instability, normal range of motion, and minimal/no meniscal or collateral ligament damage⁸ Will need surgery if tear and if person is active	Active, young athletes, additional meniscal or collateral ligament injuries⁸
Patellofemoral pain syndrome	Look for J-sign on single-leg squat. Patellar glide, tilt, grind, and apprehension tests may be positive⁵⁹	Clinical diagnosis^{22 ,59}	Physical therapy with activity modification, foot orthoses may be helpful⁵⁹	Symptoms longer than 6-12 mo despite treatment.⁵⁹Refer to PM&R
Meniscal tear	Effusion is common.¹⁴Joint line tenderness is fairly sensitive, McMurray test is specific^{14 ,83}	MRI is the imaging test of choice⁸³	Conservative treatment if asymptomatic or small and stable, and most chronic degenerative tears⁸⁴	Large complex tears, tears associated with ACL rupture, and symptoms that fail to resolve with conservative treatment.⁸⁴Refer to Orthopedic Surgery
Patellar tendinopathy	Pain on palpation of inferior pole of patella or reproduced on resisted knee extension⁸⁵	Clinical diagnosis but US can be helpful¹⁹	Eccentric physical therapy with activity modification^{19 ,86 ,87}	After failing 3 mo of conservative treatment.⁸⁸Refer to PM&R
IT band syndrome	Tenderness at lateral knee approximately 2 cm above joint line, can be increased by standing with 30° of knee flexion⁵⁵	Clinical diagnosis but MRI may be helpful⁵⁵	Activity modification, physical therapy, ice and NSAIDs⁵⁵	If poor response to conservative treatment.⁵⁵Refer to PM&R
Patellar dislocation	Usually reduces spontaneously; often large effusion, hemarthrosis, and tenderness near medial retinaculum^{44 ,89}	Weight-bearing radiographs in AP view in extension, in 45° flexion, and lateral view in 30° flexion.⁴⁴MRI is usually obtained⁹⁰	2-3 wk of immobilization with 20° of knee flexion, weight bearing as tolerated as soon as possible, followed by physical therapy⁴⁴	Inaugural dislocation, athletic patients without predisposing factors, bone avulsion, risk factors for recurrence, and recurrent dislocation⁴⁴ Refer to Orthopedic Surgery
Maisonneuve fracture	Tenderness over deltoid ligament, syndesmosis, and proximal fibula near fracture²⁸	Ankle series and dedicated films of proximal tibia²⁸	6-8 wk of casting if intact ankle mortise⁹¹	If mortise is not in anatomic alignment.⁹¹Refer to Orthopedic Surgery
Achilles tendon rupture	Palpable gap in tendon may be present. Thompson test positive in complete rupture³²	Clinical diagnosis, but MRI or US may be helpful^{31 ,32}	Casting and immobilization for 8-12 wk³¹or functional bracing with early rehabilitation⁹²	Younger and more active patients³¹ Refer to Orthopedic Surgery
Medial tibial stress syndrome	May have tenderness along distal 2/3 of posteromedial tibia. Navicular drop test may be positive²⁶	MRI can help differentiate medial tibial stress syndrome from tibial bone stress injury²⁶	Relative rest with gradual increases in activity²⁶	If conservative measures fail.²⁶Refer to PM&R
Tibial bone stress injury	Tenderness at site of reported pain with possible swelling²⁶	MRI is study of choice²⁶	Immobilization, followed by nonimpact activities²⁶	In cases of delayed healing and in athletes²⁶ Refer to PM&R and/or Ortho (Sports)
Ankle sprains	Swelling may be present. Perform anterior drawer, inversion stress, squeeze, and external rotation tests⁹³	Use Ottawa ankle rules to determine need for radiographs. If symptomatic >6 wk, CT or MRI should be considered³⁴	Rest, ice, compression, and elevation but no prolonged immobilization⁹³	Diastasis of the syndesmosis⁴³ Prolonged pain Refer to PM&R and/or Orthopedic Surgery
First MTP joint sprain	May have swelling, ecchymosis, malalignment, and tenderness at the joint³⁶	Weight bearing AP, lateral, and sesamoid axial radiographs. MRI may be helpful³⁶	Rest, ice, compression, elevation, and NSAIDs. Short leg cast with toe spica extension in slight plantar flexion may be helpful³⁶	MTP joint instability, associated fractures, chondral injury, and failed conservative treatment.³⁶Refer to Orthopedic Surgery
Fifth metatarsal fracture	Tenderness with surrounding ecchymosis and swelling⁹⁴	AP, lateral, and 45° oblique radiographs and should be repeated 10-14 d after onset symptoms³⁷	Conservative if nondisplaced, depending on fracture location and individual patient factors³⁷	Dependent on displacement, angulation, and when closed reduction is insufficient.³⁷Refer to Orthopedic Surgery
Lisfranc injury	Plantar ecchymosis and tenderness at the mid-foot⁹⁵	Weight bearing AP, lateral, and 30° oblique radiographs. MRI if clinical suspicion persists despite normal XR and CT images⁹⁵	Immobilization, rest, ice, and elevation with progression to mobility as tolerated with walking cast or controlled ankle motion boot⁹⁵	If displacement present on imaging.⁹⁵Refer to Orthopedic Surgery
Vascular
PAD	Cool extremities, absent distal pulses, audible bruit over iliac, femoral, or popliteal arteries, and nonhealing ulcers may be present⁹⁶	ABIs are inexpensive and noninvasive⁹⁶	Lifestyle modification, statin, antiplatelet therapy, cilostazol, and graduated exercise⁹⁶	Emergent revascularization for acute limb ischemia. May be appropriate for symptomatic chronic PAD.⁹⁶Refer to Vascular Surgery
DVT	Edema, erythema, warmth, and tenderness may be present⁹⁷	US when pretest probability is intermediate or high, D-dimer if low⁹⁷	Anticoagulation, determined according to specific patient factors⁹⁸	IVC filter placement may be needed if anticoagulation is contraindicated. Mechanical/pharmacomechanical treatment may be appropriate in certain patients⁹⁸
Acute compartment syndrome	Involved compartment may appear full and tense, but this is unreliable. Distal pulses may not be affected until pressure in the compartment overcomes systemic blood pressure³³	Clinical diagnosis but intracompartmental pressure monitoring may be helpful³³	Initial temporizing measures: removal of constrictive devises or wraps and leg elevation³³	Fasciotomy is definitive treatment.³³Refer to Surgery
Chronic exertional compartment syndrome	Normal examination at rest. Sensorimotor deficits may be appreciated after exercise and passive stretching may be painful²⁶	Preexertional and postexertional intracompartmental pressure testing²⁶	May be as simple as avoiding offending activity. Forefoot running may help anterior chronic exertional compartment syndrome. Botulinum toxin A intramuscular injections may be effective²⁶	Surgical fasciotomy is the mainstay of treatment²⁶ Refer to Surgery
Neuro
Morton neuroma	Observe footwear and gait and note any soft tissue abnormalities. Web space tenderness may be appreciable and plantar percussion test over affected webspace may elicit pain or paresthesia⁷⁵	US and MRI are the most commonly used imaging modalities⁷⁵	Footwear modifications and local injections with steroids, alcohols, and anesthetic agents may be effective⁷⁵	If symptoms are not improving with conservative treatment.⁷⁵Refer to PM&R
Peripheral neuropathy	Symptoms/findings typically are asymmetric, sensory symptoms are dermatomal, with possible loss of vibratory, proprioceptive, temperature, and pinprick sensation and decreased ankle reflexes⁹⁹	CBC, CMP, fasting glucose, B₁₂ and TSH, EMG or nerve biopsy may be needed⁹⁹	Treat underlying disease process. Gabapentin, topirimate, carbamazepine, pregabalin, or amitriptyline may improve pain⁹⁹	Lower extremity peripheral nerve decompression may help diffuse diabetic polyneuropathy.⁹⁹Refer to PM&R
ABI, ankle-brachial indices; AP, anteroposterior; CBC, complete blood count; CMP, complete metabolic panel; CT, computed tomography; DVT, deep vein thrombosis; EMG, electromyography; IT, Iliotibial; IVC, inferior vena cava; MRI, magnetic resonance imaging; MTP, metatarsophalangeal; NSAID, nonsteroidal anti-inflammatory drug; PM&R, physical medicine and rehabilitation; TSH, thyroid stimulating hormone; US, ultrasound; XR, X-ray.