Managing Arthrogenic Muscular Inhibition (AMI) Accompanied by Patella Baja with High-Energy Inductive Therapy (HEIT) and Advanced Radial Shockwave Noninvasive Therapy
Managing Arthrogenic Muscular Inhibition (AMI) Accompanied by Patella Baja with High-Energy Inductive Therapy (HEIT) and Advanced Radial Shockwave Noninvasive Therapy
By Rod Tomczak, MD, DPM, EdD
After multiple unsuccessful treatments, including a hylan G-F 20 injection, a 72-year-old man underwent a right total knee replacement in September 2020 to address ongoing osteoarthritis of the knee. The initial procedure was well-tolerated, and the patient began physical therapy to work toward full weight-bearing.
By January 2021, the knee had become infected with Cutibacterium acnes. Despite an aggressive course of treatment, including an extensive washout, replacement of the acrylic implant, and six weeks of IV rifampin delivered through a PICC line to the right atrium, the infection persisted. Consequently, the patient underwent another surgery to remove the implants, replace them with antibiotic spacers, and insert a new PICC line. After achieving synovasure-negative joint fluid and normalization of infection markers, a new permanent total knee replacement was performed.
Unfortunately, rehabilitation remained slow, with the patient unable to extend his knee or bear weight. By December 2023, he’d had a fifth surgery to debulk scar tissue and mobilize the knee extensor apparatus and been to 258 physical therapy sessions. The patient showed minimal improvement and could only move from a recliner to a chair-side commode using a walker.
The patient’s knee remained in a flexed position at approximately 30 degrees, severely limiting his mobility and quality of life. His surgeon recommended an above-knee amputation with a prosthesis to restore some functionality, but that would also carry a significantly reduced five-year survival rate comparable to certain cancers.
Taking charge of his recovery, the patient researched arthrogenic muscular inhibition (AMI), a condition where neural inhibition causes quadriceps activation failure, often seen after knee injuries or surgeries. With his background in running and weightlifting, the patient was able to understand an article by Sonnery-Cottet et al.1 that described varying degrees of AMI severity, from grade 0 to grade 3, and provided insights into the physical examination techniques used to classify the condition.
AMI is characterized by the inhibition of the vastus medialis obliquus (VMO) muscle, hamstring contractures, and chronic extension deficits caused by concomitant patella baja — a condition where the patella sits distal to its normal position, resulting in a hard endpoint during limited leg extension.
Grades 1 and 2 AMI typically respond well to exercise, helping to restore muscle strength and normal extension. For grade 2b cases where VMO activation is critical, patients may require up to a year of therapy, including biofeedback and electrical stimulation, to reawaken the quadriceps muscles.
Figure 1: HEIT
Figure 2: ESWT
If therapy fails, surgical interventions such as posterior arthrolysis of the knee joint capsule, patellar tendon lengthening, or patellectomy may be necessary, though these carry significant risks, including tendon rupture and knee paralysis. Thus, noninvasive modalities are preferable where applicable.
The patient began treatment using a high-energy inductive therapy (HEIT) electromagnetic device2 specifically on the quadriceps muscles, with a focus on the VMO, four times per week for 20 minutes, gradually increasing the contraction intensity. Despite starting therapy late, the patient achieved substantial hypertrophy, with a nearly two-inch increase in muscle circumference.
However, due to the initial severity of his condition, a comparison with the unaffected limb was not feasible. Over four months, the patient experienced a 50% strength gain, leading to treatment on the contralateral side and inclusion of the bilateral gastrocnemius-soleus complex in anticipation of returning to normal physical activity.
Upon starting therapy, the patient was classified as stage 3 AMI. By April 2024, he had improved but still encountered a hard endpoint roughly 15 degrees short of full extension. To address this, he was also treated with an extracorporeal shockwave therapy (ESWT) device3 on the patellar tendon, posterior knee capsule, and biceps femoris, semitendinosus, and semimembranosus tendons, which became contracted after disuse.
After one month, the patient remarkably showed significant improvement in the patella’s position, though it was still surrounded by scar tissue and in a baja position. The ESWT treatment, administered three times per week, also helped increase flexibility in the hamstring tendons. It’s important to note that ESWT is generally contraindicated for patients on anticoagulants, but this patient experienced no bleeding in the treated areas despite being on Eliquis for chronic atrial fibrillation.
After five months of HEIT and one month of ESWT, the patient experienced more significant gains than in three years of conventional physical therapy, including electric nerve stimulation. Evaluation showed that the affected limb’s VMO was only 10% smaller than the unaffected limb, and extension improved to 12 degrees.
While still insufficient for full weight-bearing, that improvement could reduce the likelihood of requiring an above-knee amputation. Early recognition and intervention are crucial to prevent patellar tendon contracture and progression to a condition necessitating amputation for mobility restoration.
High-energy electromagnetic therapy (HEIT) has proven effective as a noninvasive treatment for various musculoskeletal disorders. HEIT translates electromagnetic signals into biological ones at the cellular level, stimulating nerve, muscle fiber, and blood vessel growth through factors like fibroblast growth factor (FGF), vascular endothelial growth factor (VEGF), and bone morphogenetic proteins (BMP).
Additionally, HEIT promotes endorphin release, reducing pain and restoring normal cell membrane potentials, which aids in energy production by mitochondria and supports overall cellular function. 4-5 Thanks to its high frequency and magnetic energy levels, HEIT’s ability to stimulate deep-tissue muscles sets it apart from conventional PEMF units.
ESWT utilizes shockwaves to create microtrauma that promotes healing through neovascularization, stem cell recruitment, and growth factor release. This therapy also enhances skin elasticity, collagen production, and tissue release by breaking up fibrous bands.
The mechanical energy from shockwaves triggers biological responses through mechano-transduction, which activates cellular structures essential for healing. ESWT has demonstrated efficacy in conditions such as osteoarthritis by inhibiting cartilage degeneration and encouraging subchondral bone repair. 6
The significance of early identification of AMI cannot be overstated because it is vital to prevent patellar tendon contracture and minimize the risk of progression to a stage requiring amputation. Noninvasive therapies such as HEIT and ESWT offer substantial improvements and could potentially avert the need for more drastic interventions.
Dr. Rod Tomczak, MD, DPM, EdD, is a board-certified foot and ankle surgeon with over 40 years of experience. He has held significant academic and administrative positions, including chair of surgical care at Des Moines University, assistant professor at Ohio State University Medical Center, and founding dean roles at medical universities worldwide. Dr. Tomczak is also a member of Mensa and the International Society for Philosophical Enquiry. In his recent case study, he documents the successful treatment of AMI and patellar baja with Zimmer MedizinSystems’ emFieldPro HEIT and enPuls ESWT noninvasive modalities to avoid an above-knee amputation.
Sonnery-Cottet B, Hopper GP, Gousopoulos L, Vieira TD, Thaunat M, Fayard, JM, Freychet B, Ouanezar H, Cavaignac E, Saithna A. Arthrogenic muscle inhibition following knee injury or surgery: pathophysiology, classification, and treatment. Video Journal of Sports Medicine. 2022;2(3). doi:10.1177/26350254221086295
Zimmer Medizin Systems. emFieldPro: taking HEIT to new Heights. [Internet]. Irvine, CA: Zimmer Medizin Systems; 2024. Available from: https://zimmerusa.com/products...
Zimmer Medizin Systems. enPuls 2.0: radial pulse therapy — an effective alternative for treating chronic soft tissue pain [Internet]. Irvine, CA: Zimmer Medizin Systems; 2024. Available from: https://zimmerusa.com/products...
Stratton SA. Role of endorphins in pain modulation. Journal of Orthopaedic and Sports Physical Therapy. 1982;3(4):200-5. doi:10.2519/jospt.1982.3.4.200
Clement-Jones V, McLoughlin L, Tomlin S, Besser GM, Rees LH, Wen HL. Increased beta-endorphin but not met-enkephalin levels in human cerebrospinal fluid after acupuncture for recurrent pain. Lancet. 1980 Nov 1;2(8201):946-9. doi: 10.1016/s0140-6736(80)92106-6. PMID: 6107591.
Auersperg V, Trieb K. Extracorporeal shock wave therapy: an update. EFORT Open Rev. 2020 Oct 26;5(10):584-92. doi: 10.1302/2058-5241.5.190067. PMID: 33204500; PMCID: PMC7608508.
