Can A CAM Walker Fail? When A Patient Injures the Ipsilateral Limb During Protected Weightbearing

By Jason Miller, DPM, FACFAS, Benjamin Marder DPM, AACFAS, and Liang-Chieh Ko, DPM

Podiatrists commonly use a controlled ankle motion (CAM) walker in treating conditions involving the foot and ankle. The goal of using a CAM walker in osseous pathology is to minimize interruption of bone bridging and maximize the rate of complete recovery.^1,2 Recently, a patient presented to our office for surgical consultation related to bilateral pedal pain secondary to hallux abductovalgus deformity and underlying metatarsus adductus. This patient is a 56-year-old female with a past medical history of sleep apnea, anxiety and factor-V Leiden thrombophilia. After a thorough patient interview, physical examination and plain film radiographic review, we decided to perform a Lapidus bunionectomy with a proximal phalangeal osteotomy of the left foot. 

During the postoperative immobilization period, the patient received a novel anticoagulant for her aforementioned risk factors without complication. The patient’s first postoperative radiograph two weeks later revealed intact hardware and routine bone healing. Additionally, the patient exhibited good adherence to the recommended post-op course. In accordance with the senior author’s protocol, she transitioned to weightbearing as tolerated in a CAM walker and was provided a surgical shoe for self-transition at four weeks from surgery. 

On postoperative day 48, the patient presented to our urgent care complaining of left ankle pain following a syncopal episode the night prior. The patient stated that on the day prior, she volunteered to donate one unit of whole blood at her local Red Cross and she returned home without complications. That same evening, after finishing dinner, the patient stepped outside in her CAM walker and suddenly fainted. Fortunately, the patient regained consciousness immediately and noticed severe left ankle pain. Examination in the urgent care the following day led to a diagnosis of a bimalleolar fracture to the left ankle. When swelling allowed, the patient subsequently underwent open reduction and internal fixation of her bimalleolar ankle fracture without complication.

To date, the patient reports good recovery following both surgical procedures and serial plain film radiographs have continued to show bone union. However, the incident remains a mystery that made us wonder: what exactly happened? How would such strong, traumatizing ground reactive forces be transferred to the lower extremity despite rigid immobilization? Was the CAM walker securely fastened to her left lower extremity at the time of injury?

After we analyzed the fracture pattern, the patient appeared to suffer a supinatory deforming force on the foot and an internal deforming force on the leg (Danis-Weber type B, Lauge-Hansen SER type IV). The foot was supinated an externally-rotated talus from the inverted calcaneus. The energy from the fall continued and eventually exited medially, leaving a transverse-oblique fracture to the medial malleolus.^3,4 In order to achieve this type of fracture pattern, there must have been motion about the patient’s subtalar and ankle joints. Some may argue that recent studies have shown limitations of the Danis-Weber and Lauge-Hansen classifications. However, in this case, they are useful to analyze the pathomechanism of injury.⁵

Reviewing the patient’s narrative about the incident, she reported no loosening of the CAM walker nor did she remember whether her left ankle was outside of the boot after she recovered from the syncope. Though radiographic evaluation does not suggest poor bone stock,  we later found the patient’s serum vitamin D level to be at 34.5 ng/mL, which is “considered adequate for bone and overall health in healthy individuals” according to the National Institute of Health (MIH).⁶ Nevertheless, the senior author investigated the link between stress fracture and serum vitamin D in 2016.⁷ In this study, the senior author and colleagues found the risk of osseous compromise in a patient with a vitamin D level less than 40 ng/mL is approximately 83.02 percent. Although there was not a definitive diagnosis related to bone quality in regard to the aforementioned patient, we cannot completely rule out weakened bone integrity.

The cause of the patient’s fall was likely secondary to delayed syncope. Whole blood donation has known adverse reactions such as agitation, sweating, pallor, a sense of cold or weakness, vomiting, convulsive or delayed vasovagal syncope (VVS).⁸ Statistically speaking, the percentage of delayed, post-donation VVS is approximately 15 percent in males and 25 percent in females.⁹ Some individuals experience VVS as early as 15 minutes whereas some experience it as late as 4.5 hours after needle withdrawal.⁹ The exact cause of VVS is still unclear. However, many scholars regard it as a consequence of a series of neurophysiological events associated with traumatic venipuncture and hypotension.¹⁰ Eventually, a blood flow deficit to the brain creates transient hypoxia, resulting in a sense of weakness, pallor and loss of consciousness. Researchers have reported effective results with fluid and light nutrient replenishment in preventing orthostatic hypotension.¹¹ In our case, the patient related that VVS occurred within eight hours of blood donation and after she consumed a meal. 

As studies show, the use of joint-restricting devices such as a short leg cast or conventional CAM walker may lead to alteration of an individual’s gait such as anterior pelvic tilt, differences in hip adduction when ambulating, increase in the demand of knee flexors and possibly increased forefoot loading pressure.^12-14 Moreover, studies also indicate that the patient applies greater loading force on the shorter, non-restricted contralateral leg, which introduces instability of body posture.¹⁵ The use of a CAM walker can also create pain in a secondary site in as early as two weeks. 

Hence, for a patient’s safety and comfort, authors often strongly recommend application of a shoe leveler to the contralateral limb to compensate for altered spine and pelvic kinematics due to limb length difference.¹⁴ In this case, the patient opted to use a knee scooter for the first two weeks of postoperative recovery. Due to the rarity of the case, this will possibly be the first scientific report of ipsilateral injury to the foot and ankle while the patient is in a CAM walker. 

Did The CAM Walker Fail?

As she stated in the patient history, the patient utilized the knee scooter for two weeks and subsequently transitioned to weightbearing as tolerated in a CAM walker. However, during her second postoperative visit (3^rd week after the surgery), when we instructed the patient to replace the CAM walker with a surgical shoe in her the patient declined. The patient expressed the desire to continue weightbearing in CAM walker for better protection, which explained the prolonged postoperative use of a CAM walker in this case. In addition, the patient did not report any CAM walker malfunction. In regard to the CAM boot, the senior author used an Aircast^® AirSelect Standard device. The walker’s front panel and outer hard shell are made of high-density polyethylene with three nylon straps to secure the leg and foot. The patient denied seeing any structure compromise in the CAM boot after the fall but she felt that the walker was “loose … probably from not having enough air.” 

What About Energy Conversion During The Fall?

In 2017, Abrahamyan suggested that the force generated from a fall in a person with an estimated area of impact of 2 cm² is estimated to be 2 x 10⁴N.¹⁶ Calculating the kinetic energy (KE) of the aforementioned patient’s fall, based on Newton’s laws and the law of momentum conservation, the kinetic energy equaled approximately 1174.2328 J and the force exerted on the patient from 1.65 meters was approximately 7.1121 x 10² N. This is still much lower than 2 x 10⁴N. Also, the padded CAM walker and its hard, outer shell may have served as a protective barrier, inherently absorbing some of the impulse energy transferred to the lower extremity. 

Some researchers have demonstrated an association between elevated BMI and increased risk for hip fracture in an osteoporotic patient. However, this patient did not have a true diagnosis of osteoporosis via a DEXA scan and her BMI was 26.63 Kg/m², only 1.63 Kg/m² over the normal range published on the CDC website in 2017 (overweight = 25.0 - 29.9 Kg/m²).^17-20 

Can Skeletal Mechanical Unloading Be A Contributing Factor In This Case? 

Disuse osteoporosis is a known pathology which most commonly occurs in patients suffering from pathological immobilization such as spinal cord injury, cerebrovascular accident, muscular dystrophies or living in a zero-gravity environment.²¹ Factors that bring about various metabolic changes due to the halt of activities can include decreased bone marrow pressure, possible imbalanced neuromolecules at the junction of nerve endings and bone cells, and an increased serum level of leptin.²¹ Interestingly, a study conducted by Matsumoto and colleagues suggests that after as early as 10 weeks of complete bed rest, there is increased urine excretion of biochemical markers, which indicates bone reabsorption.²² Not only is the spike of excreted biomarkers detected, one may also observe deterioration in trabecular and cortical integrity of the distal tibia on serial computed tomography (CT) after eight weeks of non-weightbearing.²³ Our patient was immobilized for 15 days (2.1 weeks), which likely would only have a small impact on her bone equilibrium. 

Are Pathologic Lesions A Factor In This Trauma?

Radiographic evaluation of the preoperative foot X-ray did not reveal any lytic changes in the left distal tibia and fibula. The patient did report a maternal history of osteoporosis but there was no evidence of a DEXA scan being available for this patient.

As we noted above, the patient had a Factor V Leiden mutation. Interestingly enough, many hypothesize that this disorder could cause the development of osteonecrosis (OC) when venous thrombosis is entrapped in the bone, causing intraosseous hypertension that leads to hypoxic bone death.^24,25 Evaluating 29 patients with various thrombotic disorders, Gomez-Puerta and team found that 82 percent of osteonecrosis occurred in the hip, 58 percent in the knee, 37 percent in the shoulder and 13 percent in the ankle.²⁶ FVL was included in the study as one of the various thrombotic disorders. That said, the population pool in this report was small and 61 percent of the patients received corticosteroid treatment. Our patient denied receiving any corticosteroid injections. The patient also denied symptoms of osteonecrosis such as severe, gait-altering pain to her left ankle during her initial office visit. 

In Conclusion

The exact cause of this bizarre yet unfortunate accident remains unknown. Due to the nature of the event, the patient was not able to recall the details of her injury. The use of the CAM walker surely created transient abnormality in patient’s gait. However, a combination of sudden loss of consciousness and postural tone differs from losing one’s balance due to limb length differences. When a patient falls from altered gait, the reactivity of the autonomic nervous system could fire to support, prevent or even lessen the impact of the fall. Further, despite low proposed kinetic energy and additional protection from the rigid material of the boot, the patient still experienced deformation to her left ankle. This raised the question as to whether the patient properly applied the CAM boot to her left lower extremity before exiting the house. Lastly, the short period of non-weightbearing in combination with the Factor V Leiden mutation and low serum vitamin D level could have weakened the patient’s bone structure, possibly leading to porosity in the trabeculae and the cortices, and osteonecrosis caused by intraosseous hypertension and venous emboli.

Dr. Miller is the Director of the Pennsylvania Intensive Lower Extremity Fellowship at Premier Orthopaedics in Malvern, Pa. He is a Fellow of the American College of Foot and Ankle Surgeons.

Dr. Marder is a Fellow with the Pennsylvania Intensive Lower Extremity Fellowship in Malvern, Pa.

Dr. Liang-Chieh Ko is a second-year resident with the Phoenixville Hospital/Tower Health Residency Program in Phoenixville, Pa.

References

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