Date: 202109
Local time of day: 0001-0600
Location: ZZZ.TRACON, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C ZZZ; Class E ZZZ1
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Communication Breakdown; Time Pressure
Anomaly: Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control; General Physical Injury / Incapacitation
Contributing factors: Procedure; Human Factors; Weather
Primary problem: Procedure

Narrative: Trip started with FA (Flight Attendant) Brief re: Weather enroute and at ZZZ at Arrival; Passengers got same brief. Twice enroute I had FA's take their seats due to Company Alert; and Weather deviation around Utah; no issues...90nm from ZZZ; I briefed the Passengers of the weather and Arrival info; expecting a bumpy ride on the descent; and that we would be landing; and then parking at Gate XX; at XX:35 ZZZ Time; 30 minutes to landing. 20 minutes to landing; I made a PA for the FA's to take their seats; as a precaution. We were cleared direct ZZZZZ and to keep our speed up. We were then cleared to descend via the ZZZZZ and transition to 310 kts.; as we were #1. We were then given a heading for vectors to the ILSXX Approach; and descend to 12;000 ft.At 12;000 ft.; I cycled the seat belt switch and stated 'Flight Attendants prepare for landing' over the PA; early on purpose. We were then given Descend to 8;000 ft.; followed by a turn to downwind and descend to 4;000 ft. We were IMC; it was 9 degrees Celsius; 29.49; and strong winds and moderate rain. Descending from 5;000 ft. to 4;000 ft.; we encountered severe turbulence; the AP kicked off and the airplane pitched up and down erratically.I hand flew the airplane to regain control of our Flight Path; and we settled down at 4;000 ft. and re-engaged the AP. We were then given a descent to 3;000 ft.; followed by a heading to Intercept the ILSXX Approach Course; and cleared for the approach. We broke out at about 2;000 ft.; configured for a full flap landing; encountered 30 kts. headwind on Final; followed by a 10 kt. tailwind on landing; and made a normal landing.As we were rolling out; we got a call from the back (FA's); and the FO (First Officer) answered as I taxied clear of the runway. She informed me that the #2 FA hit the floor hard on her left side; and could we ask for Medics to meet us at the Gate.We were met at the Gate by 2 ZZZ Airport [Officials]; and they checked out our #2 FA. They recommended that she go to the hospital; as did I; so she could get a proper check out. It was also recommended that at least 1 other FA go with her. The FA's then left the aircraft; as did the FO.I stayed with the aircraft; so I could note in the logbook that an aircraft inspection would be needed do to our encounter with severe turbulence. FA did not go to hospital; and returned to work the next day.The 2 AFT FA's did not take their seats when instructed; by my PA: 'Flight Attendants take your seats'. FA's need to follow instructions; i.e. when told to Be Seated; then Take Your Seat.




Synopsis: Captain reported aft Flight Attendants were slow to take their seats during approach in turbulence; resulting in an injury to one Flight Attendant.